THE  LIBRARY 

OF 

THE  UNIVERSITY 

OF  CALIFORNIA 

LOS  ANGELES 


N.  S.  E.  312 


Confidential! 


SEARCHLIGHTS  AND 
SIGNAL  LIGHTS 

For  the  Instruction  of  Officers  and  Personnel  connected 

with  Searchlights 


N.WY  DEPARTMENT 
BUREAU  OF-^TEA-M  ENGINEERING 


NOVEMBER,  1918 


WASHINGTON 

GOVERNMENT  PRINTING  OFFICE 

1918 


TABLE  OF  CONTENTS. 


Chapter  1. 

Fat*. 

History  of  the  searchlight ^ 

Chapteb  2. 
High-power  searchlights 4 

Chapteh  3. 
Beck  36  and  30  inch  high-power  searchlights 24 

Chafter  4. 
Sperry  36  and  24  inch  high-power  searchlights 49 

Chapter  5. 
Qeneral  Electric  Co.  24-inch  high-power  searchlights 68 

Chapter  6. 
Anna  24-inch  high-power  searchlight 81 

Chapter  7. 
Sperry  high-power  searchlights  converted  from  general  electric  low-power  searchlights —        87 

Chapter  8. 
Low-power  searchlights 90 

Chapter  9. 
Signaling  apparatus 106 

Chapter  10. 
Types  of  operating  gears 116 

Chapter  11. 
Tables  of  general  data  on  searchlights  and  blinkers 133 

Chapter  12. 
Carbons  for  searchlights 139 

Chapter  13. 
Mirrors  for  searchlights 168 

Chapter  14. 
Care  of  modern  high-power  searchlights  and  control  gear 176 

Chapter  15. 
Vicker's  ' '  f ollow-the-pointer ' '  system  of  searchlight  control 179 

Chapter  16. 

Current  developments 190 

m 


96706U 


CHAPTER  1. 
HISTORY  OF  THE  SEARCHLIGHT. 


The  first  use  of  any  light  projector  which  could  be  called  a  searchlight  in 
any  sense  of  the  word  was  on  board  a  Union  warship  blockading  a  southern 
port  during  the  Civil  War. 

On  a  dark  night  a  Confederate  ship  attempted  to  run  the  blockade,  think- 
ing herself  secure  against  detection  on  account  of  the  blackness  of  the  night. 
Suspicion,  however,  was  aroused  on  board  the  Union  ship  and  the  first  search- 
light used  at  sea  was  brought  into  use. 

From  the  Union  ship  there  came  a  feeble,  poorly  reflected,  widely  diver- 
gent beam  of  light.  It  swTing  around,  searching  for  the  enemy,  and  finally, 
faintly  illuminated,  he  was  discovered. 

Crude  as  was  this  searchlight,  it  made  a  place  in  warfare  for  the  projector 
which  has  since  been  developed  to  a  remarkable  degree  of  efficiency.  This  first 
searchlight  was  merely  a  "limelight"  produced  by  playing  an  oxy-hydrogen 
flame  on  a  candle  of  calcium  oxide,  this  source  of  light  being  backed  by  a  crude, 
spherical,  polished  metal  mirror  which  absorbed  about  50  per  cent  of  the  total 

light. 

Shortly  after  this  came  the  first  arc  light,  which,  when  used  with  small, 
spherical  metal  mirrors,  was  useful  up  to  a  maximum  range  of  perhaps  300 
yards. 

The  next  military  use  of  searchlights  was  at  the  siege  of  Paris  (1870-71) 
in  which  arc  lights  were  used.  They  bm-ned  vertically  and  the  entire  arc  and 
flame  was  used  as  the  source  of  light,  rather  than  using,  as  is  the  present  prac- 
tice, only  the  very  brilliant  positive  crater.  The  arc  current  was  about  10 
amperes.  This  light  was  mounted  behind  a  rather  expensive  and  complicated 
system  of  lenses  and  prisms  invented  by  Fresnel.  It  had  previously  found 
application  in  lighthouses,  and  because  of  the  good  results  obtained  by  this 
system  in  that  service,  it  was  tried  on  searchlights.  However,  on  account  of 
its  complication,  expense,  and  low  efficiency,  it  could  not  stand  in  the  face 
of  later  inventions. 

In  1876,  Col.  Mangin  brought  out  his  silvered  glass  reflector  which  gave 
excellent  results  and  was  the  forerunner  of  modern  searchlight  mirrors.  For 
a  long  time  it  had  been  recognized  that  a  parabolic  silvered  glass  mirror 
would  be  the  best  reflector  obtainable,  but  at  that  time  it  was  impossible  to 
grind  one.  Spherical  mirrors  were  useless  because  of  unavoidable  distortion 
of  the  beam.  Mangin's  reflector  consisted  of  a  mirror  ^\^th  its  front  surface 
and  back  surface  spherical,  but  with  different  radii  and  not  concentric.  This 
corrected  spherical  aberration. 

So  successful  was  this  mirror  that  it  still  finds  a  fairly  wide  application 
for  small  lights. 

66438—18 1  1 


2  THE   SEARCHLIGHT. 

The  limitation  of  the  Mangin  mirror  was,  however,  its  small  effective 
angle.  It  could  not  utilize  more  than  half  the  available  light.  Tliis  was 
due  to  the  fact  that  the  mirrors  were  too  thick  and  too  clumsy  if  they  were 
ground  to  subtend  more  than  90°  of  arc.  Moreover,  the  parallchsm  of  the 
reflected  light  could  not  be  maintained  at  large  angles. 

Attempts  were  made  to  overcome  these  difficulties  by  building  up  the 
reflector  from  a  large  number  of  separately  ground  rings,  called  meniscus 
rings.  Tliese  were  not  successful  on  account  of  the  trouble  of  lining  up  the 
separate  rings  accurately  and  adjusting  them  to  have  the  same  focus. 

In  the  year  1886  Schuckert,  of  Nuremburg,  succeeded  in  producing  the 
first  plate  glass  parabolic  mirror.  This  was  the  final  stop  in  the  development 
of  the  optical  system  of  searclilights.  The  advantages  of  the  parabohc  re- 
flector were  immediately  recognized  and  this  system  has  been  in  almost  uni- 
versal use  from  1886  until  the  present  day. 

The  historical  outhno  above  has  referred  mainly  to  the  development  of 
the  optical  features.  Equally  important  in  connection  with  the  searchlight 
is  the  development  of  the  source  of  light.  The  history  of  this  phase  is  very 
brief.  The  fii-st  useful  searchlight  in  1870  employed  a  direct  current  pure 
carbon  arc,  and  searchlights  are  still  employing,  for  the  most  part,  the  same 
pure  carbon  arc.  For  over  50  j^ears  the  carbon  arc  stood  unchallenged  as 
the  brightest  illurainant  known.  Tliis  period  was  not,  however,  without 
progress.  The  first  crude  lights  were  small  vertical  arcs  of  very  low  amperage. 
They  were  necessarily  used  in  a  vertical  position  for  increased  steadiness  of 
burning.  The  horizontal  arc  was  almost  an  impossibility  at  that  time,  due  to 
its  fhckering  and  instability. 

At  about  the  time  of  the  Mangin  mirrors  a  compromise  was  made  between 
the  steadiness  of  tlie  vertical  arc  and  the  increased  light  flux  on  the  mirror 
of  the  horizontal  arc.  Tliis  was  accomplished  by  burning  the  carbons  at  an 
angle  of  20°  to  30°,  so  that  the  positive  crater  (the  uppermost  carbon  being 
positive)  burned  off  at  an  angle  and  presented  its  face  moi-e  nearly  normal 
to  the  reflector.  This  arrangement  was  used  for  over  20  years,  and  even  now 
these  searchlights  may  occasionally  be  found  on  board  the  older  ships. 

This  arc  was  slowlj'  disjJaced  by  tlie  horizontal  arrangement  of  the  car- 
bons. With  the  improvement  in  carbon  manufacture,  the  horizontal  arc 
was  finally  made  to  burn  properly.  This  horizontal  arrangement  has  since 
been  universally  used  in  searcldiglits  employing  the  pure  carbon  arc. 

Until  quite  recently  no  notable  improvements  were  made  in  the  source 
of  light.  Thick  pure  carbon  electrodes  were  used  and  the  improvements 
consisted  mostly  in  arranging  the  lamp  to  get  the  best  results  and  throw  the 
greatest  amount  of  light  upon  the  mirror,  and  in  improving  the  feeding 
mechanisms  and  electrodes.  The  crater  which  forms  in  the  positive  carbon 
is  the  point  of  maximum  intrinsic  briffiancj'  (greatest  light  intensity  per  unit 
area)  and  ttiis  was  faced  toward  the  mirror.  The  shadow  cast  by  the  nega- 
tive carbon  and  holder  was  reduced  by  reducing  the  diameter  of  the  negative 
carbon  and  plating  it  heavily  \vith  copper.  This  copper  plating,  however, 
melted  and  formed  slag,  preventing  even  burning  or  causing  short  circuits. 

Beyond  a  certain  point,  an  increase  in  current  density  produced  no  increase 
in  intrinsic  brilliancy,  but  merely  served  to  increase  the  diameter  of  the  crater, 


THE  SEAECHLIGHT.  3 

which  was  of  no  advantage.     The  augmentmg  power  of  a  searchlight  may  be 
roughly  expressed  mathematically: 

Square  of  diameter  of  mirror 
Square  of  diameter  of  crater. 

B\*  this  it  is  seen  that  an  increase  in  the  diameter  of  the  crater  is  undesirable 
unless  the  diameter  of  the  mirror  be  iucreased  in  the  same  ratio.  The  size  of 
the  mirror  is  limited  by  practical  considerations  to  about  36  inches  for  use  on  ships, 
so  it  is  readily  seen  that  this  fixes  the  size  of  the  positive  carbon  for  most  efficient 
work.  That  is,  the  upper  limit  of  efficiency  had  been  reached  years  ago  for 
this  type  of  low  power  lamp. 

The  extreme  range  at  which  a  target  could  be  seen  with  the  aid  of  binoculars 
when  illuminated  with  the  best  Navy  searchlight  of  this  type  was  about  4,000 
yards.  Good  illumination  could  not  be  obtained  at  a  greater  range  than  3,000 
yards,  nor  could  range  finder  readings  be  taken  accurately  at  much  over  2,000 
yards. 

With  the  increase  in  effective  ranges  and  accuracy  of  guns  and  torpedoes, 
and  the  increasing  speed  of  ships,  this  type  of  searchhght  became  rapidy  less 
effective  in  comparison.  It  was  developed  to  its  highest  point  and  people  had 
to  make  the  best  possible  use  of  the  limited  light  available. 

Very  recently,  about  1914,  there  came  the  modern  high-power  searchlight. 
In  size  and  general  appearance  it  is  similar  to  the  old  low-power  light,  the 
difference  occurring  in  the  lamp,  which  employs  much  smaller  carbons  of  a 
special  kind,  having  a  core  of  light  emitting  materials.  Greater  current  densi- 
ties are  also  employed. 

In  the  new  type  of  searchlight  the  crater  in  the  positive  carbon  is  much 
smaller  and  much  deeper  than  in  the  old  tj-pe,  and  its  intrinsic  brilliancy  is  far 
greater.  Going  back  to  the  equation  of  augmenting  power,  it  is  seen  that  the 
diameter  of  the  crater  "d"  has  been  decreased  and  with  great  increase  in  ivr- 
trinsic  hriUiancy,  bringing  the  efficiency  of  the  searchlight  to  twice  its  former 
value.  Kanges  may  be  taken  easily  at  over  4,000  yards  with  sharper  definition 
of  target,  objects  may  be  plainly  seen  at  6,000  yards,  and  at  8,000  yards  the 
target  is  plain  when  binoculars  are  used.  Searchlight  power  was  therefore 
doubled  by  one  improvement. 

The  color  of  the  beam  of  the  high-power  searchlight  inclines  to  blue,  making 
the  beam  of  the  old  type  look  yellow  b}'  comparison.  The  blue  gives  sharper 
definition  and  better  illumination  of  objects  painted  war  color.  There  is  also 
less  dispersion  of  the  beam,  together  with  greater  penetrating  power.  High- 
power  searchlights  are  made  for  the  Xavy  in  36-,  30-,  and  24-inch  diameters. 


CHAPTER  2. 
HIGH-POWER  SEARCHLIGHTS. 


GENERAL  DESCRIPTION. 

High-powor  searchlights  differ  from  the  low  power  in  the  size  and  rate  of 
burning  of  the  carbons,  the  current  densitj',  the  composition  of  the  positive 
electrode  which  has  a  special  core,  the  intrinsic  brilliancy  of  the  crater,  and 
the  greater  arc  temperature  requiring  special  provision  for  cooling.  There  are 
other  differences  which  are  mostly  mechanical  and  do  not  differ  materially 
in  prmciple  from  older  types. 

There  are  four  types  of  high-power  searchlights  now  in  use,  the  Beck 
alcohol  "cooled"  light,  manufactured  by  the  General  Electric  Co.,  the  General 
Electric  Co.'s  air-cooled  light,  the  Sperry  light,  manufactured  by  the  Sperry 
Gyroscope  Co.,  and  the  Anna  light.  All  have  carbons  of  small  diameter  and 
rapid  consumption,  and  deep  crater  positive  carbons.  The  Beck  light  has 
alcohol  burners  fitted  beneath  the  carbons;  the  alcohol  flame  envelopes  the 
exposed  part  of  the  carbons  and  serves  to  keep  the  temperature  of  the  carbons 
down  to  a  safe  workmg  value.  The  air-cooled  lights  employ  a  sj-stem  of 
forced  draft,  the  air  being  blown  along  the  carbons  througli  i)assages  in  the 
carbon  holders  and  around  drum,  or  of  induced  draft,  the  circulation  of  air 
being  produced  by  a  fan  in  the  top  of  the  drum.  These  searchlights  work  with 
a  steady,  quiet  arc  and  require  little  attention  while  running. 

The  Sperry  and  General  Electric  air-cooled  lights  are  suitable  for  searching 
the  zenith  and  may  be  elevated  and  used  continuously  at  any  angle,  while, 
as  stated  later,  the  Beck  light  is  not  suitable  for  high-angle  use.  The  air- 
cooled  lights  have  further  advantages  in  being  less  complicated  and  requiring 
less  time  and  trouble  to  start  and  less  attention  while  running. 

The  illuminating  power  and  target  visibility  range  is  about  the  same  for 
all  high-power  lights  of  the  same  size. 

Specifications  for  high-power  searchlights  are  given  below. 

Specifications   for  36-inch   Hiqh-Power   Seabchliohts    for   Use   in  the  United  State 

Navy. 

[february  26,  1917.] 

1.  General  specifications  for  the  inspection  of  material  issued  by  the  Navy  Department, 
in  effect  at  date  of  opening  of  bid,  shall  form  part  of  these  specifications. 

2.  The  searchlights  will  be  designated  by  the  following  types  and  vdU  be  designed  to  be 
operated  on  a  line  voltage  of  120  unless  otherwise  specified. 

(a)  Distant  mechanical  control,  type  A,  B,  C,  or  D. 

(6)  Distant  electrical  control. 

(c)  Distant  electrical  and  mechanical  control. 

4 


THE  SEABCHLIGHT.  5 

(i)  Distant  electrical  control,  on  truck. 

(e)  Distant  electrical  control,  anti-aircraft,  on  truck. 

3.  General  for  all  types. 

(J)  Drum. — The  drum  tt-ill  be  made  of  brass  and  have  openings  which  permit  of  easy  access 
to  the  lamp  mechanism  and  mirror.  All  openings  in  the  drum  will  be  so  covered  as  to  exclude 
wind  and  rain  and  permit  the  light  to  be  operated  without  flickering  when  the  wind  blows  at 
the  rate  of  30  statute  miles  per  hour.  The  covers  will  be  so  placed  on  the  drum  that  when  the 
shutter  is  closed  and  the  light  is  burning  there  will  be  no  light  \Tsible  at  a  distance  of  10  meters 
(about  33  feet)  in  any  direction  from  the  searchlight.  A  calibrated  ground  glass  finder  will  be 
fitted  in  the  drum  in  a  convenient  position,  and  will  give  an  upright  full-sized  image  of  the  arc 
on  the  ground  glass.  It  will  also  show  the  image  of  each  carbon  and  be  marked  to  indicate  the 
correct  position  for  same,  so  that  the  arc  can  be  kept  in  correct  length  and  in  the  focal  point  of 
the  mirror.  Pro\Tsion  will  be  made  for  varying  the  intensity  of  the  image  on  the  ground-glasa 
finder  to  meet  day  and  night  conditions  of  operation.  It  will  be  capable  of  permitting  operator 
to  watch  the  arc  without  any  light  being  visible  at  a  distance  of  200  meters  (about  656  feet)  from 
the  searchlight.     A  metal-hinge  cover  over  ground-glass  finder  will  be  provided. 

Two  small  arc  weld  or  electric  smoked  glass  obser\'ing  openings,  ^vith  metal  covers,  will  be 
placed  in  a  convenient  section  of  the  drum.  They  will  permit  a  clear  and  unblurred  view  of  the 
arc  and  make  \'isible  the  electrode  holders. 

A  direct  current  ammeter  of  approved  tj-pe  in  a  weatherproof  case  with  a  hinged  or  sliding 
door  will  be  provided.  It  will  have  an  illuminated  dial,  and  the  meter  scale  will  go  at  least 
100  per  cent  higher  than  the  normal  current  of  the  arc.  It  will  be  so  located  on  the  searchlight 
aa  to  be  accessible  to  the  operator. 

The  drum  will  be  so  ventilated  that  during  a  continuous  run  of  one  set  of  carbons  the  tem- 
perature rise  vrill  not  endanger  the  mirror  or  any  other  parts  of  the  searchlight. 

The  ventilation  shall  be  sufficient  to  prevent  the  deposit  of  enough  fumes  on  the  mirror 
during  10  hours  usage  to  materially  impair  its  reflecting  power.  It  will  be  of  sufficient  capacity 
to  carry  off  heat  at  such  a  rate  that  with  the  shutter  closed  for  20  minutes  with  the  arc  burning 
under  normal  conditions  the  temperature  shall  not  endanger  the  mirror.  The  ventilating  system 
will  not  cause  any  flickering  of  the  arc.  It  will  be  possible  to  open  the  drum  doors  while  the 
arc  is  burning. 

The  drum  will  be  so  designed  that  the  lamp  mechanism  can  be  easily  removed.  If  a  cooling 
gas  be  used  with  the  carbon  flame  the  tank  containing  the  liquid  from  which  the  gas  is  produced 
will  be  placed  on  the  outside  of  drum  and  high  enough  to  allow  the  liquid  to  flow  into  the  vapor- 
izing apparatus  by  the  force  of  gravity. 

(g)  Front  door  and  strips. — The  front  door  shall  consist  of  a  light  composition  ring  which  will 
be  reaiiily  removable  from  the  drum,  and  be  designed  to  hold  the  positive  carbon  holder,  front- 
door strips,  iris  shutter,  and  Venetian  blind  shutter.  'U'hen  in  place  it  will  be  so  supported  by 
springs  and  rollers  to  eliminate  breakage  due  to  gun  fire. 

The  front  door  strips  will  be  securely  mounted  in  a  composition  ring  and  each  strip  will  be 
readily  removable  from  the  ring.  They  will  be  of  clear,  white,  plate  glass  with  surfaces  parallel 
and  highly  polished.  The  edges  of  strips  will  be  at  right  angles  to  the  surfaces  and  have  a  ground 
glass  finish.  The  outside  diameter  of  strips  will  be  thirty-seven  and  three-sixteenths  inches 
(37t^  inches)  and  the  thickness  of  strips  one-fourth  of  an  inch  (}  inch). 

T\'here  parallel  strips  are  furnished  they  will  be  12  in  number  and  reiilforced  by  metal 
strengthening  strips,  to  withstand  the  shock  of  gunfire. 

WTiere  radial  strips  are  furnished  they  will  be  16  in  number  and  all  strips  will  be  identical  in 
shape  and  reinforced  as  nece,<!sary  to  withstand  the  shock  of  gun  fire. 

The  composition  ring  holding  front  door  strips  will  be  securely  mounted  in  the  front  door 
and  be  easily  removable. 

The  front  door  will  have  attached  to  it  the  positive  carbon  tube  supported  rigidly  by  a  tripod 
arrangement  attached  to  the  ring.  It  shall  be  easily  removable.  The  tube  will  be  insulated  on 
the  inside  and  have  weatherproof  cap  which  ^vill  be  easily  removable. 

(h)  Dome. — The  dome  shall  consist  of  a  composition  mirror  ring  to  which  are  secured  a  sheet 
copper  mirror  covering  and  two  lifting  handles.  The  dome  will  be  fastened  by  clamps  to  the 
drum  in  a  manner  so  as  to  eliminate  breakage  due  to  gunfire.  These  clamps  to  be  80  designed 
as  to  enable  the  operator  to  readily  detach  the  dome. 


6  THE  SEARCHLIGHT. 

(t)  Trunnion  arms. — The  trunnion  arms  will  be  made  of  bronze,  pressed,  or  cast  steel  and  will 
be  of  sufficient  height  to  permit  the  drum  to  be  elevated  at  least  30°  above  or  30°  below  the  hori- 
zontal train.  They  will  be  securely  fastened  to  the  rotating  section  of  the  base.  A  suitable  scale 
graduated  in  degrees  will  be  provided  to  indicate  the  amount  of  elevation  of  the  drum.  A  small 
covered  light  with  switch  will  be  placed  over  the  poiiiter  so  as  to  illuminate  the  pointer  and  scale 
immediately  under.  If  searchlight  is  designed  to  search  the  zenith  and  is  not  equipped  with 
an  inclined  mirror  in  front  of  barrel,  the  trunnion  arms  will  be  designed  to  permit  the  drum  to 
be  elevated  100°  above  or  30°  below  the  horizontal  train. 

(j)  Base. — The  base  will  consist  of  two  parts — a  stationary  lower  part  and  a  rotating  upper 
part.  The  base  will  be  hollow,  circular  in  shape,  and  made  of  iron  or  composition.  A  circidar 
flat  graduated  (degrees)  scale  will  be  securely  fastened  to  the  stationary  part  of  the  base  and  an 
indicating  pointer  ^vill  be  placed  on  the  rotating  section  to  indicate  the  angle  of  train  of  the  search- 
light. A  small  covered  light  with  swit<h  will  be  placed  over  the  pointer  so  as  to  illuminate  the 
pointer  and  scale  immediately  under.  The  base  will  contain  a  clamp  arrangement  for  holding 
the  drum  in  any  fixed  angle  of  train.  Hand  wheels  for  the  control  of  the  searchlight  will  be  placed 
on  the  base  or  other  convenient  position  as  approved. 

(jb)  Mirror  and  inirror  holder. — The  mirror  will  be  in  strict  accordance  with  advance  sheet 
33-b,  copies  of  which  can  be  obtained  upon  application  to  the  Bureau  of  Steam  Engineering. 
The  mirror  will  be  mounted  in  the  composition  mirror  ring.  An  asbestos  material  approximately 
i  centimeter  (0.1968.5  inch)  thick  and  2.5  centimeters  (0.98425  inch)  wide  will  be  placed  between 
the  mirror  ring  and  mirror  to  assure  a  snug  fit.  A  space  of  J  centimeter  (0.19685  inch)  lietween 
the  edge  of  mirror  and  mirror  ring  to  allow  for  any  expansion  of  the  mirror  due  to  heat  will  be 
filled  in  with  asbesto.s  material. 

(I)  Lamp  mechanisvi.— The  lamp  will  be  constructed  so  that  the  operator  has  easy  access  to 
all  working  parts.  The  lamp  will  be  designed  for  both  automatic  feed  (with  device  for  goveniing 
the  speed)  and  hand  feed  for  carbons,  and  the  cliange  in  feed  will  be  easily  accomplished  while 
lamp  is  in  operation.  The  automatic  feed  will  be  operated  by  a  motor.  Tlie  lamp  will  have 
both  hand  and  electrical  de\'ice8  for  rotating  the  positive  carbon.  A  water-tight  s\»'itch  conven- 
iently located  will  be  i)ro\aded  for  momentarily  stopping  the  rotation.  The  feeding  arrange- 
ment will  be  so  designed  as  to  maintain  an  arc  voltage  between  values  of  70  and  80  volts  and  to 
maintain  an  arc  length  of  about  2.2  centimeters  (0.866  inch)  at  150  amperes.  The  lamp  mechanism 
will  maintain  the  crater  of  the  positive  carlion  at  the  focus  of  the  mirror  with  a  maximum  variation 
of  not  greater  than  1  millimeter  (0.04  inch)  on  each  side  of  the  actual  focus.  The  lamp  and  drum 
will  be  so  designed  that  new  carbons  may  be  put  in  and  light  started  up  within  a  period  of  eight  min- 
utes from  the  time  the  light  is  turned  off.  The  lamp  will  be  designed  for  150  amperes  current  and 
the  carbon  holders  shall  be  so  designed  that  there  will  not  be  a  wastage  of  more  than  20  centimeters 
(7.874  inches)  of  carbon.  The  positive  carbon  holder  will  be  mounted  in  a  horizontal  position 
and  the  negative  carbon  holder  will  be  placed  at  such  an  angle  with  the  horizontal  center  line  of 
the  positive  carbon  holder  as  to  give  the  best  burning  condition  of  the  carbon  and  maximum 
intensity  of  light  flux  on  mirror.  If  searchlight  is  designed  to  search  the  zenith  and  is  not 
equipped  with  an  inclined  mirror  in  front  of  barrel,  a  tray,  sufficiently  large  to  catch  all  chips 
from  the  carbons  to  prevent  them  from  falling  on  mirror,  but  which  will  not  block  off  more  than 
15  per  cent  of  the  beam,  will  be  furnished. 

The  connections  inside  the  lamp  mechanism  will  be  firmly  secxu'ed  in  place  and  the  entire 
lamp  mechanism  will  withstand  a  dielectric  test  of  1,500  volts  A.  C.  applied  for  one  minute. 

(m)  Shutters. — All  shutters  will  be  made  of  light,  non-corrosive  material.  A  suitable  hand- 
wheel  for  operating  the  iris  shutter  through  gears  will  be  located  on  the  side  of  the  drum  where 
it  is  easily  accessible  for  the  operator.  The  Venetian  blind  shutter  will  be  operated  by  a  handle 
located  on  the  side.  All  searchlights  will  be  supplied  with  iris  shutters  and  searchlights  as  speci- 
fied also  with  Venetian  blind  shutters. 

(n)  Rheostats. — The  rheostat  will  be  of  the  unit  t>'pe  and  must  be  sufficiently  inclosed  for  pro- 
tection against  injury  and  at  the  same  time  allow  effective  ventilation.  A  suitable  insulated 
board  containing  resistance  contacts  and  rheostat  handle  will  be  mounted  on  the  rheostat.  The 
rheostat  will  consist  of  two  sections,  a  variable  and  fixed  resistance.  The  variable  resistance 
will  be  divided  into  at  least  10  steps,  each  step  giving  when  hot  approximately  a  drop  of  1  volt 
when  a  normal  current  of  150  amperes  flows  through  them.  The  elements  will  be  thoroughly 
protected  against  corrosion  in  such  a  manner  as  not  to  give  off  objectionable  smoke  and  securely 
fastened  in  the  supporting  frame  at  a  sufficient  number  of  points  to  prevent  damage  from  shocks, 


THE  SEARCHLIGHT.  7 

and  the  method  of  mounting  will  permit  a  ready  connection  of  the  leads  and  removal  of  grids  for 
repairs.  A  pan  will  be  installed  underneath  to  catch  any  molten  metal  or  displaced  pieces  should 
the  elements  become  melted  or  broken  at  any  point.  The  total  resistance  from  cold  to  hot  shall 
not  exceed  12  per  cent  of  cold  resistance.  Conngctions  between  rear  of  panel  and  resistance  unit 
will  be  made  with  commercial  fireproof  wire.  The  temperature  rise  on  frame  will  not  exceed  125°  C . 
The  rheostat  will  withstand  an  overload  of  50  per  cent  in  amperes  for  a  period  of  10  minutes  con- 
tinuously •without  damage. 

(o)  Carbons. — The  carbons  will  be  suitable  for  150  amperes  current  and  will  be  hard,  fine,  and 
homogeneous  in  texUire;  straight  and  of  accurate  circular  cross  section.  They  will  have  no  defects 
such  as  cracks  and  blisters,  and  when  burning  at  150  amperes  current  will  give  a  steady  light  without 
hissing,  spluttering,  or  flickering,  and  will  not  throw  off  any  chips  and  will  give  off  but  a  small 
percentage  of  ash.  The  positive  and  negative  carbons  will  be  respectively  16  millimeters  (0.62992 
inch)  and  11  millimeters  (0.43307  inch)  in  diameter  with  an  allowance  of  plus  or  minus  1  millimeter 
(0.03937  inch).  They  will  be  straight  and  not  vary  more  than  1.5  millimeters  (0.059  inch)  from 
any  point  from  a  straightedge  placed  in  contact  with  carbon  ends.  When  carbons  are  burning 
with  a  ciuTont  of  150  amperes  arc  voltage  75  and  arc  length  about  2.2  centimeters  (0.86614  inch) 
the  maximum  light  intensity  will  be  at  least  100,000  candlepower.  The  intrinsic  brilliancy 
when  the  carbons  are  burning  under  normal  conditions  shall  be  at  least  500  candlepower  per  square 
millimeter  (0.0155  square  inch).  The  carbons  shall  be  of  sufficient  length  to  burn  two  and  one-half 
hours  continuously.  The  carbons  to  be  composed  of  such  material  that  when  burning  under 
normal  conditions  the  searchlight  beam  shall  be  of  a  bluish  white  color. 

Bidders  shall  guarantee  satisfactory  operation  of  searchlight  ■with  carbons  of  American  manu- 
facture and  shall  give  price  at  which  they  will  furuish  suitable  carbons  for  a  period  of  two  years. 
Acceptance  tests  of  searchlight  will  be  made  with  carbons  of  American  manufacture. 

4,  T3rpes  of  control. 

(p)  Distant  mechanical,  Type  A. — The  controller  will  consist  of  two  separate  composition 
gear  boxes  in  accordance  with  Bureau  of  Steam  Engineering  plan  No.  19-S-2832-L.  Copies  of 
this  plan  can  be  obtained  upon  application  to  the  Bureau  of  Steam  Engineering,  Navy  Department, 
Washington,  D.  C. 

(5)  Distant  mechanical,  Type  B. — The  controller  will  consist  of  one  composition  gear  box  and 
handwheels,  mounted  on  composition  pedestal  and  connected  by  concentric  pipe  shafts  to  search- 
light. The  searchlight  will  be  controlled  by  three  handwheels  mounted  on  gear  box  and  con- 
nected to  shafts.  Two  handwheels  on  opposite  sides  of  box  will  control  the  angle  of  train  and  the 
third  handwheel  will  control  the  angle  of  elevation  and  depression.  Illiuminated  dials  will  be 
installed  in  gear  box  to  indicate  the  number  of  degrees,  elevation,  or  depression,  and  also  the  angle 
of  train.  Means  will  be  provided  for  disengaging  the  mechanical  control  and  operating  the  search- 
light by  handwheels  located  thereon. 

(r)  Distant  mechanical,  Type  C. — The  controller  will  consist  of  gear  box,  handwheels  for  con- 
trol, illuminated  dials  and  means  for  disengaging  from  searchlight  as  specified  under  (5)  but 
designed  to  mount  in  a  single  searchlight  trestle  work  tower,  with  handwheels  mounted  outside 
of  tower  sides  and  connected  to  gear  box  by  shafting. 

(s)  Distant  mechanical,  Type  D. — The  controller  will  consist  of  gear  box  illuminated  dials,  and 
means  for  disengaging  from  searchlight  as  specified  under  {q)  but  designed  to  mount  in  a  double 
searchlight  trestlework  tower  with  two  handwheels,  one  for  control  of  elevation  and  depression, 
and  one  for  control  of  angle  of  train,  mounted  outside  of  tower  sides  and  connected  to  gear  box  by 
shafting. 

(t)  Distant  electrical. — The  distant-electrical  controller  will  consist  of  two  separate  composition 
boxes  mounted  on  composition  pedestals,  the  design  of  the  electric  controller  will  be  such  as  to 
move  the  searchlight  without  jerk.  The  controller  will  be  capable  of  training  the  searchlight 
at  a  minimum  speed  of  3°  per  minute  and  a  maximum  speed  of  360°  per  minute.  It  will  also  be 
capable  of  elevating  or  depressing  the  searchlight  at  minimum  speed  of  3°  per  minute  and  a  maxi- 
mum speed  of  180°  per  minute.  One  controller  will  control  elevation  and  depression  and  one 
will  control  the  angle  of  train.  The  controller  will  be  as  light  in  weight  as  possible  without  sacri- 
ficing strength  and  satisfactory  operation.  Means  will  be  pro\'ided  for  disengaging  the  electrical 
control  and  operating  searchlight  by  hand. 

(«)  Distant  electrical  and  mechanical. — This  type  of  control  will  consist  of  controllers  of  both 
types  described  in  paragraph  4  (p)  and  4  (q).    Means  will  be  pro\ided  for  disengaging  either  the 


8  THE  SEAHCHLIGHT, 

distant  electrical  control  or  distant  mechanical  control  or  both,  and  operating  searchlights  with 
either  type  or  by  hand. 

(v)  Distant  electrical,  antiaircraft. — This  controller  will  be  similar  to  the  one  described  in 
paragraph  4  (q)  but  with  one  unit  designed  to  tjain  the  searchlight  and  the  other  unit  to  either 
elevate  the  drum  or  rotate  in  either  direction  the  ring  supporting  the  mirror  suspended  in  front  of 
searchlight.  Means  will  be  provided  for  disengaging  the  portable  electric  control  and  operating 
the  searchlight  and  the  mirror  by  hand. 

5.  Material. — All  working  parts,  Ulterior  bolts,  nuts,  pins,  screw^s,  springs,  brush  holders, 
and  studs  will  be  of  non-corrodible  material  thoroughly  sheradized,  heavily  copper  plated,  or 
otherwise  thoroughl>-  coated  to  prevent  corrosion. 

6.  Insulation. — All  insulation  shall  be  of  approved  insulating  material.  Hard  rubber  and 
porcelain  are  not  approved. 

7.  Motors  and  auxiliaries. — .\11  motors  and  auxiliarici  will  be  in  strict  accordance  ^vith 
Specifications  17A3,  latest  issue. 

K.  Wire. — .Ml  wire,  except  fire  proof  and  magncl  wire,  will  bo  in  strict  accordance  with  Spoci- 
tications  ]')C\,  latest  issue,  and  magnet  wire  will  be  in  strict  accordance  with  Specifications  1.5\V2b 
unless  otherwise  specified. 

!).  Finish. — All  exterior  surfaces  of  searchlight  will  be  finis'hed  in  battleship  gray. 

10.  Tool  box. — Contractor  will  furnish  a  complete  list  of  tools  and  appliances,  as  per  bureau 
drawing  9-S-SK-2686-L  (or  equivalent  list)  for  operation  of  searchlight  and  will  furnish  these 
tools  and  accessories  in  strong  hardwood  box  in  accordance  with  the  requirements  of  Specifications 
17A3,  late.'^t  issue. 

11.  Spare  parts. — Each  searchlight  will  be  supplied  with  a  complete  set  of  spare  parts  for 
operation  of  searchlight  for  a  period  of  three  years,  as  per  bureau  drawing  9-S-SK-2686-L  (or 
equivalent  list).  Spare  parts  will  be  boxed  in  accordance  with  the  requirements  of  Specifications 
17A3,  lates;'  s.'ue. 

12.  Instructions. — Contractor  will  furnish  with  each  searchlight  a  pamphlet  containing 
instructions  for  operation  and  care  of  searchlight. 

13.  Bids. — Bids  will  not  be  considered  for  searchlights  of  type  which  have  not  been  submitted 
for  test  at  the  navy  yard,  New  York,  and  have  operated  satisfactorily  and  been  approved  as 
acceptable  under  these  specifications  prior  to  date  of  opening  of  bids. 

14.  Drawings. — Bids  will  be  accompanied  by  duplicate  blue  prints  showing  assembly 
views  giving  over-all  dimensions  and  weights  of  iirincipal  jiarts,  also  additional  detailed  plans, 
if  neces-sary  to  give  a  clear  understanding  of  the  apparatus  to  be  furni.shed. 

After  preliminary  acceptance  of  the  .searchlights,  a  complete  set  of  first-class  assembly  and 
detail  drawings  on  tracing  cloth  will  be  supplied  to  the  Bureau  of  Steam  Engineering,  Navy  Depart- 
ment, \Va.shington,  D.  C.  The  drawings  must  be  accurate  in  everj'  respect,  and  must  represent 
all  details  of  the  searchlights  as  they  will  appear  when  finally  accepted  by  the  Government. 

If  tracings  of  any  of  the  plans  referred  to  above  are  on  file  at  the  Bureau  of  Steam  Engineer- 
ing, and  are  correct  in  all  respects  for  the  material  in  question,  duplication  of  the  same  is  not 
required.  They  shall,  however,  be  referred  to  in  bid  by  both  manufacturer's  and  bureau's  file 
numbers. 

All  drawings  will  be  made  to  scale  which  will  be  definitely  indicated  on  each  plan. 
(w)  All  tracings  will  conform  to  the  following  sizes: 
27  by  20  inches. 
27  by  40  inches. 
27  by  60  inches. 
27  by  80  inches. 
27  by  84  inches. 
The  vertical  dimension  of  tracings  in  all  cases  will  be  27  inches. 

Specifications  for  24-1  nxh  High- Power  Searchlights  for  Use  in  the  United  States  Navy. 

(JUNE  5,  1917.] 

1.  General  specifications  for  the  inspection  of  material  issued  by  the  Navy  Department 
in  effect  at  date  of  opening  of  bid  shall  form  part  of  these  specifications. 

2.  The  searchlights  will  be  designated  by  the  following  types  and  will  be  designed  to  be 
operated  on  a  line  voltage  of  120  unless  otherwise  specified. 

(a)  Hand  control;  antiaircraft. 

(6)  Distant  electrical  control;  antiaircraft. 


THE  SEAECHLIGHT.  9 

(c)  DiMant  mechanical  control;  antiaircraft,  type  A,  B,  C,  or  D. 

3.  General  for  all  types. 

(/)  Drum. — The  drum  will  be  made  of  brass  and  have  openings  which  permit  of  easj-  access 
to  the  lamp  mechanism  and  mirror.  All  openings  in  the  drum  will  be  so  covered  as  to  exclude 
wind  and  rain  and  permit  the  light  to  be  operated  without  flickering  when  the  wind  blows  at  the 
rate  of  30  statute  miles  per  hour.  The  covers  will  be  so  placed  on  the  drum  that  when  the  shutter 
is  closed  and  the  light  is  burning  there  will  be  no  Light  visible  at  a  distance  of  10  meters  (about 
33  feet)  in  any  direction  from  the  searchlight.  A  calibrated  ground-glass  finder  will  be  fitted  in 
the  drum  in  a  convenient  position  and  ivill  give  an  upright  full-sized  image  of  the  arc  on  the 
ground  glass.  It  will  also  show  the  image  of  each  carbon  and  be  marked  to  indicate  the  correct 
position  for  same,  so  that  the  arc  can  be  kept  in  correct  length  and  in  the  focal  point  of  the  mirror. 
Pro^^sion  will  be  made  for  vanrTiig  the  intensity  of  the  image  on  the  ground-glass  finder  to  meet 
day  and  night  conditions  of  operation.  It  will  be  capable  of  permitting  operator  to  watch  the  arc 
without  any  light  being  visible  at  a  distance  of  200  meters  (about  6.56  feeti  from  the  searchlight. 
A  metal  hinge  cover  over  ground-glass  finder  will  be  provided.  A  sighting  arrangement,  con- 
sisting of  two  suitable  gun  sights  mounted  on  left-hand  side  of  barrel  facing  mirror,  will  be  pro"vided. 

Two  small  arc -weld  or  electric  smoked-glass  obser\'ing  openings  T\-ith  metal  covers  will  be 
placed  in  a  convenient  section  of  the  drum.  They  will  permit  a  clear  and  unblurred  vievr  of  the 
arc  and  make  vTsible  the  electrode  holders. 

The  drum  will  be  so  ventilated  that  during  a  continuous  run  of  one  set  of  carbons  the  tem- 
perature rise  will  not  endanger  the  mirror  or  any  other  parts  of  the  searchlight. 

The  ventilation  shall  be  suflBcient  to  prevent  the  deposit  of  enough  fumes  on  the  mirror 
during  10  hours  usage  to  materially  impair  its  reflecting  power.  It  will  be  of  sufficient  capacity 
to  carry  off  heat  at  such  a  rate  that  with  the  shutter  closed  for  20  minutes  with  the  arc  burning 
under  normal  conditions  the  temperature  shall  not  endanger  the  mirror.  The  ventilating  sj'stem 
will  not  cause  any  flickering  of  the  arc.  It  will  be  possible  to  open  the  drum  doors  while  the 
arc  is  burning. 

The  drum  will  be  so  designed  that  the  lamp  mechanism  can  be  easily  removed. 

Handles  for  control  of  searchlight  will  be  placed  at  the  back  of  barrel. 

(g)  Front  door  and  strips. — The  front  door  shall  consist  of  a  light  composition  ring  which 
will  be  readily  removable  from  the  drum,  and  be  designed  to  hold  the  positive  carbon  holder, 
front-door  strips,  iris  shutter,  and  venetian-blind  shutter.  When  in  place  it  will  be  so  supported 
by  springs  and  rollers  as  to  eliminate  breakage  due  to  gunfire. 

The  front-door  strips  will  be  securely  mounted  in  a  composition  ring  and  each  strip  will  be 
readily  removable  from  the  ring.  They  will  be  of  clear,  white,  plate  glass  with  surfaces  parallel 
and  highly  polished.  The  edges  of  strips  will  be  at  right  angles  to  the  surfaces  and  have  a  ground- 
glass  finish.     The  outside  diameter  of  strips  will  be  2-5-^  inches  and  the  thickness  of  strips  J^  inch. 

^^Tiere  parallel  strips  are  furnished  they  will  be  10  in  number  and  reinforced  by  metal  strength- 
ening strips  to  withstand  the  shock  of  gunfire. 

Where  radial  strips  are  furnished  they  will  be  12  in  number,  and  all  strips  will  be  identical  in 
shape  and  reinforced  as  necessary  to  withstand  the  shock  of  gunfire. 

The  composition  ring  holding  front-door  strips  will  be  securely  mounted  in  the  front  door 
and  be  easily  removable. 

The  front  door  will  be  fitted  for  passing  through  positive  carbon.  It  shall  be  ea.sily  removable. 
The  positive  carbon  will  be  incased  in  a  tube  which  will  be  insulated  on  the  inside  and  have 
weatherproof  cap  which  will  be  easily  removable. 

(h)  Dowe. — The  dome  shall  consist  of  a  composition  mirror  ring  to  which  are  secured  a  sheet 
copper  mirror  covering  and  two  lifting  handles.  The  dome  will  be  fastened  by  clamps  to  the  dnmi 
in  a  manner  so  as  to  eliminate  breakage  due  to  gunfire.  These  clamps  to  be  so  designed  as  to 
enable  the  operator  to  readily  detach  the  dome. 

(i)  Trunnion  arms. — The  trunnion  arms  will  be  made  of  (bronze)  pressed  or  cast  steel  and  will 
be  sufficient  height  to  permit  the  drum  to  be  elevated  at  least  100°  above  or  30°  below  the  hori- 
zontal train.  They  will  be  securely  fastened  to  the  rotating  section  of  the  base.  A  suitable  scale 
graduated  in  degrees  will  be  pro\ided  to  indicate  the  amount  of  elevation  of  the  drum.  A  small 
covered  light  with  switch  will  be  placed  over  the  pointer  so  as  to  illuminate  the  pointer  and  scale 
immediately  under.  One  trunnion  arm  will  carry  a  suitable  clamp  for  securing  searchlight  at 
any  degree  of  elevation  or  depression. 

(j)  Base. — The  base  will  consist  of  two  parte.  A  stationary  lower  part  and  a  rotating  upper 
part.     The  base  will  be  hollow,  circular  in  shape  and  made  of  iron  or  composition.     A  circular 


10  THE  SEABCH  LIGHT. 

flat  graduated  (degrees)  scale  w-ill  be  securely  fastened  to  the  stationary  part  of  the  base  and  an 
indicator  pointer  will  be  placed  on  the  rotating  section  to  indicate  the  angle  of  train  of  the  search- 
light. A  email  covered  light  with  switch  will  be  placed  over  the  pointer  so  ae  to  illuminate  the 
pointer  and  scale  immediately  under.  The  base  will  contain  a  clamp  arrangement  for  holding  the 
drum  in  any  fixed  angle  of  train. 

(t)  Mirror  and  mirror  holder. — The  mirror  will  be  in  strict  accordance  withSpecification  17-M -3a 
of  February  1,  1917,  copies  of  which  can  be  obtained  upon  application  to  the  Bureau  of  Steam 
Engineering.  The  mirror  will  be  mounted  in  the  composition  mirroring.  An  asbestos  material 
approximately  \  centimeter  (0.19G85  inch)  thick  and  2.5  centimeters  (0.98425  inch)  wide  will 
be  placed  between  the  mirror  ring  and  mirror  to  assure  a  snug  fit.  \  space  of  J  centimeter  (0.19685 
inch)  between  the  edge  of  mirror  and  mirror  ring  to  allow  for  any  expansion  of  the  mirror  due  to 
heat  will  be  filled  in  mth  asbestos  material.  Where  mirror  is  not  manufactured  by  bidder,  the 
bureau  will  be  informed  in  bid  the  name  of  the  firm  manufacturing  same  and  also  supplied  with 
a  copy  of  contract. 

(/)  Lamp  mechanism. — The  lamp  will  be  constructed  so  that  the  operator  has  easy  access  to 
all  working  parts.  The  lamp  will  be  designed  for  both  automatic  feed  (with  de\'ice  for  governing 
the  speed)  and  hand  feed  for  carbons,  and  the  change  in  feed  will  be  easily  accomplished  while 
lamp  is  in  operation.  Pro%-ision  will  be  made  for  cooling  both  carbons  with  air.  The  automatic 
feed  will  be  operated  by  a  motor.  The  lamp  will  have  both  hand  and  electrical  devices  for  rotating 
the  positive  carbon.  A  water-tight  switch  conveniently  located  will  be  provided  for  momenta- 
rily stopping  the  rotation.  The  feeding  arrangement  will  be  so  designed  as  to  maintain  an  arc 
voltage  between  values  of  55  and  60  volts  and  to  maintain  an  arc  length  of  about  |  inch  at  75 
amperes.  The  lamp  mechanism  mil  maintain  the  crater  of  the  positive  carbon  at  the  focus  of  the 
mirror  with  a  maximum  \aiiation  of  not  greater  than  1  millimeter  (0.04  inch)  on  each  side  of  the 
actual  focus.  The  lamp  and  drum  will  be  so  designed  that  new  carbons  may  be  put  in  and  light 
started  up  within  a  period  of  8  minutes  from  the  time  the  light  is  turned  off.  The  lamp  will  be 
designed  for  75  an'peres  current  and  the  carbon  holders  shall  be  so  designed  that  there  will  not 
be  a  wastage  of  more  than  20  per  cent.  The  positive  carbon  holder  va\l  be  mounted  in  a  hori- 
zontal position  and  the  negative  carbon  holder  will  be  placed  at  such  an  angle  with  the  horizontal 
center  line  of  the  positive  holder  as  to  give  the  best  burning  condition  of  the  carbon  and  maximum 
intensity  of  light  flux  on  mirror. 

A  tray  sutliciently  large  to  catch  all  chips  from  the  carbons  to  prevent  them  from  falling  on 
mirror,  but  which  will  not  block  off  more  than  15  per  cent  of  the  beam,  will  be  furnished. 

The  connections  inside  the  lamp  meclianism  will  be  firmly  secured  in  place  and  the  entire 
lamp  mechanism  will  withstand  a  dielectric  test  of  1,500  volts  alternating  current  applied  for 
one  minute. 

(m)  Shutters. — All  shutters  will  be  made  of  light  noncorrosive  material.  A  suitable  hand- 
wheel  for  operating  the  iris  shutter  through  gears  will  be  located  on  the  side  of  the  drum  whore 
it  is  easily  accessible  for  the  operator.  The  Venetian  blind  shutter  will  be  operated  by  a  handle 
located  on  the  side.  All  searchlights  will  be  supplied  with  iris  shutters  and  Venetian  blind 
shutters. 

(n)  Rheostats. — The  rheostat  will  be  of  the  unit  type  and  must  be  sufficiently  inclosed  for 
protection  against  injur}-,  and  at  the  same  time  allow  effective  ventilation.  A  suitable  insulated 
board  containing  resistance  contacts  and  rheostat  handle  will  be  mounted  on  the  rheostat.  The 
rheostat  will  consist  of  two  sections,  a  variable  and  fixed  resistanre.  The  varialile  resistance 
will  1)0  divided  into  at  least  10  steps,  each  step  giving  when  hot  approximately  a  drop  of  one  volt 
when  a  normal  current  of  75  amperes  flows  through  them.  The  elements  will  be  thoroughly 
protected  against  corrosion  in  such  a  manner  as  not  to  give  off  objectionable  smoke,  and  securely 
fastened  in  the  supporting  frame  at  a  sufficient  number  of  points  to  prevent  damage  from  shocks, 
and  the  method  of  mounting  will  permit  a  ready  connection  of  the  leads  and  removal  of  grids 
for  repairs.  A  pan  -will  be  installed  underneath  to  catch  any  molten  metal  or  displaced  pieces 
should  the  elements  become  melted  or  broken  at  any  point.  The  total  resistance  from  cold  to 
hot  shall  not  exceed  12  per  cent  of  cold  resistance.  Connections  I'etween  rear  of  panel  and  re- 
sistance unit  will  be  made  with  commercial  fireproof  wire.  The  temperature  rise  on  frame  will 
not  exceed  125°  C.  The  rheostat  will  withstand  an  overload  of  50  per  cent  in  amperes  fos  a  period 
of  10  minutes  continuously  without  damage. 

(o)  Carbons — The  carbons  will  lie  s\iitable  for  75  amperes  current  and  will  be  hard,  line,  and 
homogeneous  in  texture;  straight  and  of  accurate  circular  cross  section.     They  will  have  no  defects 


THE   SEAECHLIGHT.  11 

such  as  cracks  and  blisters  and  when  burning  at  75  amperes  current  will  give  a  steady  light  without 
hissing,  sputtering,  or  flickering  and  will  not  throw  off  any  chips  and  will  give  off  but  a  small 
percentage  of  ash.  The  positive  and  negative  carbons  ^vill  be  respectively  11  millimeters 
(0.43307  inch)  in  diameter  with  an  allowance  of  plus  or  minus  1  millimeter  (0.03937  inch).  They 
will  he  straight  and  not  vary  more  than  1..5  millimeters  (0.059  inch)  from  any  point  from  a  straight- 
edge placed  in  contact  with  carbon  ends.  When  carljons  are  liurning  with  a  current  of  75  amperes 
arc  voltage  58  and  arc  length  about  ^  inch  the  minimum  useful  mean  spherical  candlepower 
on  mirror  24.000.  The  intrinsic  brilliancy  when  the  carlions  are  V)urning  under  normal  condi- 
tions shall  lie  at  least  300  candlepower  per  square  millimeter.  The  carbons  shall  be  of  sufficient 
length  to  burn  two  and  one-half  hours  continuously.  The  carlions  to  be  composed  of  such  material 
that  when  burning  under  normal  conditions  the  searchlight  beam  shall  be  of  a  bluish  white  color. 
Bidders  shall  guarantee  satisfactorj'  operation  of  searchlight  with  carbons  of  American  manu- 
facture and  shall  give  price  at  which  they  will  furnish  suitable  carbons  for  a  period  of  two  years. 
Acceptance  tests  of  searchlight  will  be  made  with  carbons  of  American  manufacture. 

4.  Types  of  control. 

(p)  Distant  mechanical,  type  A. — The  controller  will  consist  of  two  separate  composition  gear 
boxes  in  accordance  with  Bureau  of  Steam  Engineering  plan  No.  19-S-2832-L.  Copies  of  this 
plan  can  be  obtained  upon  application  to  the  Bureau  of  Steam  Engineering,  Na^'J'  Department, 
Washington,  D.  C. 

(q)  Distant  mechanical,  type  B. — The  controller  will  consist  of  one  composition  gear  box  and 
handwheels,  mounted  on  composition  pedestal  and  connected  by  concentric  pipe  shafts  to  search- 
light. The  searchlight  will  be  controlled  by  three  handwheels  mounted  on  gear  box  and  con- 
nected to  shafts.  Two  handwheels  on  opposite  sides  of  box  will  control  the  angle  of  train  and 
the  third  handwheel  will  control  the  angle  of  elevation  and  depression.  Illuminated  dials  will 
be  installed  in  gear  Ijox  to  indicate  the  numl^er  of  degrees  elevation  or  depression  and  also  the 
angle  of  train.  Means  will  be  provided  for  disengaging  the  mechanical  control  and  operating 
the  searchlight  by  handwheels  located  thereon. 

(r)  Distant  meBianical,  Type  C. — The  controller  will  consist  of  gear  box,  handwheels  for 
control,  illuminated  dials,  and  means  for  disengaging  from  searchlight  as  specified  tinder  (g)  but 
designed  to  moimt  in  a  single  searchlight  trestle-work  tower,  with  handwheels  mounted  outside 
of  tower  sides  and  connected  to  gear  box  by  shafting. 

(s)  Distant  mechanical.  Type  D. — The  controller  will  consist  of  gear  box,  ilhuninated  dials,  and 
means  for  disengaging  from  searchlight  as  specified  under  {q)  but  designed  to  mount  in  a  double 
searchlight  trestle-work  tower,  with  two  handwheels,  one  for  control  of  elevation  and  depression, 
and  one  for  control  of  angle  of  train,  mounted  outside  of  tower  sides  and  connected  to  gear  box 
by  shafting. 

{t)  Distant  electrical. — The  distant-electrical  controller  will  consist  of  two  separate  composition 
boxes  mounted  on  composition  pedestals;  the  design  of  the  electric  controller  will  be  such  as  to 
move  the  searchlight  without  jerk.  The  controller  will  be  capable  of  training  the  searchlight  at  a 
minimum  speed  of  3°  per  minute  and  a  maximum  speed  of  360°  per  minute.  It  viill  also  be 
capable  of  elevating  or  depressing  the  searchlight  at  minimum  speed  of  3°  per  minute  and  a  maxi- 
mum speed  of  180°  per  minute.  One  controller  ^vill  control  elevation  and  depression  and  one  will 
control  the  angle  of  train.  The  controller  will  be  as  light  in  weight  as  possible  without  sacrificing 
strength  and  satisfactory  operation.  Means  will  be  provided  for  disengaging  the  electrical  control 
and  operating  searchlight  by  hand. 

5.  Material. — All  working  parts,  interior  bolts,  nuts,  pins,  screws,  springs,  brush  holders, 
and  studs  will  be  of  noncorrodible  material  thoroughly  shearadized,  heavily  copper  plated,  or 
otherwise  thoroughly  coated  to  prevent  corrosion. 

6.  Insulation. — All  insulation  shall  be  of  approved  insulating  material.  Hard  rubber  and 
porcelain  are  not  approved. 

7.  Motors  and  auxiliaries. — All  motors  and  auxiliaries  will  be  in  strict  accordance  with 
Specifications  17A3,  latest  issue. 

8.  Wire. — All  wire  except  fireproof  and  magnet  wire  will  be  in  strict  accordance  with  Speci- 
fications 15C1,  latest  issue,  and  magnet  wire  will  be  in  strict  accordance  with  Specifications  15W2b 
unless  otherwise  specified. 

9a.  Finish. — All  exterior  surfaces  of  searchlights  will  be  finished  in  battleship  gray. 
10.  Tool  Box. — Contractor  will  furnish  a  complete  list  of  tools  and  appliances,  as  per  bureau 
drawing  9-S-SK-2686-L  (or  equivalent  list),  for  operation  of  searchlight  and  will  furnish  these 


12 


THE  SEABCHLIGHT. 


tools  and  accesaories  in  strong  hardwood  box  in  accordance  with  the  requirementa  of  Specifications 
17A3,  latest  issue. 

11.  Spare  Farts. — Each  searchlight  will  be  supplied  with  a  complete  set  of  spare  parts  for 
operation  of  searchlight  for  a  period  of  three  years,  as  per  bureau  drawing  9-S-SK-268&-L  (or 
equivalent  list).  Spare  parts  will  be  boxed  in  accordance  with  the  requirementa  of  Specifications 
17A3,  latest  issue. 

12.  Instructions. — Contractor  will  furnish  with  each  searchlight  a  pamphlet  containing 
instructions  for  operation  and  care  of  searchlight. 

13.  Drawings. — Bids  will  be  accompanied  by  duplicate  blue  prints  showing  assembly  views 
giving  over-all  dimensions  and  weii;ht8  of  principal  parts,  also  additional  detailed  plans,  if  nec- 
essary to  give  a  clear  understanding  of  the  apparatus  to  be  furnished. 

After  preliminary  acceptance  of  the  searchlights,  a  complete  set  of  first-class  assembly  and 
detail  drawings  on  tracing  cloth  will  be  supplied  to  the  Bureau  of  Steam  Engineering,  Navy  De- 
partment, Washington,  D.  C.     The  drawings  must  be  accurate  in  every  respect,  and  must  repre- 
sent all  details  of  the  searchlights  as  they  will  appear  when  finally  accepted  by  the  Government. 
If  tracings  of  any  of  the  plans  referred  to  above  are  on  file  at  the  Bureau  of  Steam  Engineering, 
and  are  correct  in  all  respects  for  the  material  in  question,  duplication  of  the  same  is  not  required. 
They  shall,  however,  be  referred  to  in  bid  by  both  manufacturer's  and  bureau's  file  numbers.    ' 
All  drawings  will  be  made  to  scale,  which  will  be  definitely  indicated  on  each  plan. 
(w)  All  tracings  will  conform  to  the  following  sizes: 
27  by  10  inches. 
27  by  40  inches. 
27  by  60  inches. 
27  by  80  inches. 
27  by  84  inches. 
The  vertical  dimension  of  tracings  in  all  cases  will  be  27  inches. 


Accessories,  spare  parts,  and  tools  for  high  power  Back  36-  and  SO-inch  starchlighls. 

(Searchlights:  Each  to  be  wired  complete  sind  supplied  with  fixed  and  varialjlc  rheostat  and  iris  shutter.  Orders  for 
material  will  specify  whether  mechanical  or  electrical  control,  and  if  required,  whether  fitted  with  signaling  shutter, 
antiaircraft  features,  and  whether  mounted  on  truck.  Where  electrical  control  is  specified,  100  feet  of  cahlc,  couplings, 
and  controller  will  be  furnished  with  each  searchlight.] 


Spare  parts  (separately  6oxed). 

Spare  lamp  complete  (each  in  box) 

Set  glass  front  door  strips  (each  set  inseparte  box) 

rarbons,  positive  (10  in  each  box) 

Carbons,  negative  (10  in  each  box) 

Spare  parti. 
Box: 

Containing  the  following 

Set,  all  mica  insulation  for  lamp 

Relay  magnet  coll 

Feeding  magnet  coil 

Starting  motor  shunt  field  coil 

Starting  motor  series  field  coil 

Feeding  motor  field  coil 

Vaporizer  heating  unit 

Positive  and  negative  contacts  for  carbon  heads  .set. . 

B  urncr  for  lam  p 

Positive  and  negative  carbon  head  rollers set.. 

Rheostat  bushings  for  supporting  rods 

Carbon  head  noses pairs. . 

Rheostat  grids 

Lifting  bars pairs. . 

Brush  holders  and  3  additional  springs,  each  kind  and 
type,  for  ventilating,  lamp  starting,  and  feeding 
motors 

Armature  for  lamp-starting  motor 

Armature  for  lamp-fooding  motor 

.\rmature  for  lamjvventilating  motor 

Field  coil  for  ventilating  motor 

Alcohol  strainers set. . 

Test  rods do 

Fuses 


Number  installed  per  vessel. 


1 
1 

150 
150 


1 

2 

300 

300 


1 
4 

«00 
600 


6 

8 

2 

2 

6 

8 

900 

1,200 

900 

1 

1,200 

1 

1 

(! 

8 

3 

4 

3 

4 

3 

4 

3 

4 

3 

4 

S 

10 

3 

4 

i     2- 

3 

2 

3 

■  * 

4 

2 

2 

15 

20 

2 

2 

I 

1 

2 

2 

2 

2 

2 

2 

9 

2 

1 

1 

12 

16 

10 


2 

10 

l,.soo 

1,500 


2 

12 
1,800 
1,800 


1 

12 
« 
« 
6 
« 
4 
4 
6 

14 
6 
6 
2 

.10 
3 


1 

2 
2 
2 
2 
4 
1 
24 


THE  SEAECHLIGHT. 


13 


The  following  will  be  included  in  the  above-mentioned  box  when  electically  controlled 
Bearchlights  arc  specified: 


Number  installed 

Mr  veessl. 

1 

2 

4 

6 

8 

10 

12 

1 

2 

2 

3 

3 

4 

6  contact  fingers  for  controller  elevating  cylinder sets. . 

6  contact  Angers  for  controller  training  cylinder do 

2 

3 

4 

5 

6 

7 

' 

7  arcing  contacts  or  segments  for  controller  elevating  cylin- 

der                                                  sets.. 

1 

1 

1 
1 

2 

2 

2 
2 

3 

3 

2 
2 

4 

4 

2 
2 

5 
5 

2 

2 

6 

7  arcing  contacts  or  segments  for  controller  training  cylinder. 

6 

23  pieces  mica  insulation  for  controller  elevating  cylinder, 

3 

23  pieces  mica  insulation  for  controller  training  cylinder,  .sets. . 

3 

3  all  springs  for  controller set . . 

1 

2 

2 

2 

3 

Field  coils,  each  kind  and  type,  for  elevating  and  traming 

1 

2 

2 

2 

3 

Armature,  each  kind  and  type,  for  elevating  and  training 

1 
1 

2 

1 

2 
1 

2 
I 

3 

1 

Brush  holder  and  3  extra  springs  for  training  motor 

1 

1 

1 

1 

I 

2  brushes  for  elevating  motors set . . 

2 

6 

8 

10 

12 

2  brushes  for  traming  motors do 

2 

6 

8 

10 

12 

Fuses  for  control  circuit 

8 

16 

24 

32 

40 

48 

Starting  resistance  for  elevating  motor sets. . 

1 

2 

2 

2 

3 

Starting  resistance  for  training  motor do 

1 

2 

3 

Tool  boxes  (furnished  as  accessories  with  each  searchlight) . . . 

2 

6 

8 

10 

12 

Each  contaming  the  following: 

I  pair  blue  glass  goggles. 

1  pair  carbon  cutters. 

2  wrenches  for  Xo.  8/36  and  No.  10/30  nuts. 

1  large  dust  brush. 

1  small  dust  brush. 

1  focusing  screen. 

2  reamers  for  carbon  heads. 

1  set  (2)  ventilating  motor  brushes. 

1  set  (17)  all  springs  for  lamp. 

1  observing  screen,  made  up  of  1  red  and  1  green  col- 

ored glass  mounted  in  a  wooden  frame. 

1  hand-feed  socket  wrench. 

Accessories,  spare  parts,  and  tools  for  high-power  36  and  24  inch  air-cooled  searchlights 

Searchlights:  Each  searchlight  wUl  be  wired  complete  and  supplied  with  fixed  and  variable  rheostat  and  iris  shutter. 
Orders  for  material  will  specify  tvpj  of  control,  whether  fitted  \vith  antiaircraft  features  and  whether  mounted  on  truck. 
When  electrical  control  is  specified,  100  feet  of  cable,  couplings,  and  controller  will  be  furnished  with  each  searchUght. 
When  mechanical  control  is  specified,  the  necessary  shafts,  in  length  as  specified,  and  controller  will  be  furnished  with 
each  searchlight.] 


Number  per  vessel. 


10 


12 


Spare  parts  (each  in  separate  bo.x): 

Lamp  complete 

Sets  glass  front-door  strips 

Carbons  (positive),  2-5  per  bo.x 

Carbons  (negative  L  2.5  per  box 

Spare  parts  (all  m  one  box) 

All  insulation  for  lamp  and  drum,  including  collector 
rings  in  base set . . 

Field  coils  for  feeding  motor 

Field  coils  for  lamp  motor 

Field  coils  for  ventilating  motor 

Coil  for  magnet 

Positive  and  negative  contacts  for  carbon  heads set.. 

Posiliveand  negative  carbon  head  rollers do.. 

Armatiue  for  lamp  motor 

Armature  for  ventilating  motor 

Brush  holders  and  3  additional  springs,  each  kind  and 
type  for  vent  ilating  and  feeding  motors 

Quartz  bushings 

Thermostat  mirror 

Front  cap  and  stray  light  shield  for  positive  head 

Asbestos  washers  for  bushings  (large  hole) 

.\sbestos  washers  for  bushings  (small  hole) 

Thermostat  coil 

Thermostat  condenser 

Thermostat  strips set . . 

Arc  voltage-regulating  coil 

Positive  head  front  casting 

Negative  head  casting 

Insulated  coupling  for  positive  and  negtivc  feed  rods 

Rheostat  bushings  for  supporting  rods 

Rheostat  grids  (fixed  element) 

Rheostat  grids  (variable  element) 

Rheostat  for  negative  feed  control 

Pawls  for  lamp set  (3) . . 

Negative  head  cups 

Fuses  for  azimuth  and  training  scale  lamps 

Insulating  compound  for  screw  head  (i-pound  in  can) 

Lifting  bars pairs. . 


1 

1 

150 

130 

1 

1 
1 
1 
1 
1 
1 
1 
2 
1 

2 
12 
2 
6 
12 
12 
1 
2 
1 
1 
1 
1 
1 
2 
2 
2 
1 
1 
2 
4 
1 
1 


1 

2 

300 

300 

1 

2 
2 
2 
2 
2 
2 
2 
2 
1 

4 
24 
4 
12 
24 
24 
1 
4 
2 
1 
2 
2 
1 
2 
4 
4 
1 
1 
4 
8 
2 
1 


1 
4 

600 

600 

1 

4 
2 
2 
2 
2 
2 
2 
3 
2 

4 

48 

8 

24 

48 

48 

1 

6 

4 

1 

2 

2 

2 

2 


2 
6 

900 

900 

1 

6 
3 
3 
3 
3 
3 
3 
3 
2 


1,200 

1,200 

1 


2 

10 

1,500 

1,500 

1 

10 
5 
5 
5 
5 
5 
5 
5 
3 

10 

120 

20 

60 

120 

120 

2 

10 

10 

2 

5 

5 

3 

4 

20 

20 

2 

5 

12 

20 

5 

2 


2 
12 

1,S00 

1,800 

1 

12 
6 
6 
6 
6 


6 
4 

12 

144 

24 

72 

144 

144 

2 

10 

12 

2 

6 

6 

4 

6 

24 

24 

2 

6 

12 

24 

6 

3 


14 


THE   SEARCHLIGHT. 


When  electrically  controlled  eearchlighu  are  specified,  the  following  additional  spare  parts 
will  be  included  in  the  above  "spare-part"  box. 


Number  per  vessel. 


10  12 


Spanner  wrench  for  coupling 

Field  colls  (each  kind  and  type)  (or  elevating  motor 

Field  coils  (each  kind  and  type)  for  training  motor 

Armature  for  elevating  motor 

Armature  fur  training  motor 

Brush  holders  and  set  s  o(  all  springs  lor  elevating  motor 

Brush  holders  and  sets  of  all  springs  for  training  motor 

Brushes  (complete)  for eU'viiting  motor sets.. 

Brushes  (complete)  for  training  motor do 

All  springs  for  controller do 

All  contact  fingers  and  contacts  for  controller do 

All  insulation  tor  controller  parts do 

Tools  (furnished  as  accessories  with  each  searchlight)  ..boxes.. 
Each  containing  the  following: 

One  pair  carbon  cutters. 

Two  wrenches  for  No.  8-36  and  No.  10-30  nuts. 

One  chamois  skin 

One  large  dustbrush. 

One  small  dustbrush. 

One  duster  in  case. 

One  set  ventilating  motor  brushes. 

Two  sets,  lamp  motor  brushes. 

One  focusing  screw. 

One  pair  carbon  tongs. 

One  set,  carbon  head  gauges  for  aligning  heads. 

Two  reamers  for  carbon  heads. 

One  suitable  observing  screen  in  frame. 

One  pawl  wrench. 

One  ground  glass  for  finder. 

One  hand  feed  socket  wrench. 

One  oil  can,  J  pint. 

One  pair  6-mcri  side  cutting  pliers. 

One  pair  8-inch  flat  nose  pliers. 

One  pair  8- inch  combination  side  cutting  gas  pliers. 

One  li-inch  screw  driver. 

One  4i-inch  screw  driver. 

One  S-'inch  screw  driver. 

One  G-inch  bicycle  wrench. 

One  O-inch  monkey  wrench. 

One  l-pound  can  graphite  compound. 

One  J-pound  ball  pecn  machinist's  hammer. 

One  jVinch  diameter  pin  punch. 

One  8-inch  half  round  hasp. 

One  grease  gun  (1  ounce). 

One  sheet  000  crocus  paper. 


4 
4 

12 

12 
12 
12 
3 
7 
3 
12 


Tliere  are  shown  on  the  following  pages  curves  taken  from  a  test  on  high 
and  low  power  searchlight  carbons.  The  tests  were  made  with  the  aid  of  a 
spectrophotometer,  an  instrument  which  is  a  combination  of  a  spectroscope 
and  a  photometer.  By  it,  the  comparative  intensity  of  light  of  any  wave 
length  may  be  measured,  as  the  instrument  is  so  constructed  that  light  at  any 
part  of  the  visible  spectrum  may  be  compared  with  the  photometer  standard. 
The  calibration  is  in  microns,  the  unit  of  wave  length.  (A  micron  equals 
0.001  millimeter.) 

A  comparison  of  the  curves  for  high-power  carbons  with  those  for  low- 
power  carbons  will  show  the  immense  advance  made  when  the  modern  high- 
power  searchlight  was  produced  (figs.  1  to  9).  Not  only  was  the  intensity 
greatly  increased,  but  the  spectrophotometer  showed  the  light  to  be  of  the 
most  advantageous  wave  length,  i.  e.,  color. 


THE   SEAECHLIGHT. 


15 


Plate 

No.l. 

W.OO 

1 

A 

TYPICAL 
SPECTRUM  INTENSITIES 

\ 

CARBONS  FOR  G.E.Co.  HIGH  POWER  ARC 

FOR 

NAVALSEARCHLIGHTS 

\ 

THESE  CURVES  AHETHEAVERAGEOf  THE  RESUaSOBIAWE!) 
FROMSEVERALREPRESEHTATOE  SAMPLES  OF  CARBOKS 
SUBMITTEDATVARIOUS  TIMES  FORTESTS 

3S.00 

I          note: 

\                    CURVEAlSINTENSlTVOFTOTALARC 
^                    CORVE  B  IS  INTEKSITYOf  FLAME0NLY4  CARBOHTIPS 

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Fig.  1. 


16 


THE  SEAEOHUGHT. 


Plate 

No.5. 

1 

SPECTRUM  INTENSITY 

OF 

HIGH  POWER  CARBON  ARC 

FOR 

NAVAL  SEARCHLIGHTS 

MAOt   BY 
1E  SPERRY  GV«05C0PE  COMPANY,  N.YOR 

CARBONS  MADE  BY 
1E  NATIONAL  CARBON  CO.,CLEVELAND,  0 

RC  NORnALATlMAHf>7SV0LnAKLENGTH22C^ 

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THE   SEARCHLIGHT. 


17 


Plate 

No  5* 

» 

SPECTRUM  INTENSITY 

OF 

HIGH  POWER  CARBON  ARC 

FOR 

NAVAL  SEARCHLIGHTS 

MADE  BY 

TME  SPERRY  GYROSCOPE  CO.,NEW  YORK 

CARBONS  MADE  BY 

THE  NATION  AU  CARBON  CO.,  CLEVEL  AN  D,  0. 
ARC  NORMAL  AT  ISO  AMP.  75  V01I5  ARC  LENGTN2?Mei 
READINGS  FOR TOTALINTENSITYTAKENATO-ANGLES 

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Fig.  3. 


18 


THE  SEAECHLIGHT. 


Plate 

No.tO 

*2  50 
40  CO 

nso 

35.00 

TYPICAL 
SPECTRUM  INTENSITV 

LOW  POWER  CARBON  ARC  ">•  NAVAL 
SEARCHLIGHTS 

SHOWINSTDTALINTENSITYo'ARCCRATEB  CARBON  TIPS 
4  FLAME 

READINGS  TAKEN  AT  30  ANGLE 

ARC  NORMAL  AT  IIOAHP  fcOvOLTS.ARC  LENGTH  US  INCHES 
aRBONS  M4DEBY  NATIONALCARBON  CO  CLEVELAND.OMIO 

AND 

>  77.50 

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note: 

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Fig.  4. 


THE  SEAECHUGHT. 


19 


Plate  No.ll 

SPECTRUM  INTENSITY 
CARBON  ARC  ro" 

36" NAVAL  SEARCHLIGHTS 

MADE  BY 

GFNFR41  Fl  FfTRICmMPANY AHO 

5UPERCEEDED  BYTHE  HIGH  INTENOTY  ARC 

N 

ARCNORMALATI10AMPS.60VOnSARCLEKEIHL75l«alES 
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READmGSF0RFLAMESS'ni>STAK[HAT9O°AH0LE 

13.0 

\ 

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(KITE: 

CUFNEA  ISINTENSITY  OF  TOTAL  ARC 
CURVEB1S1NTENS1TYOFFLAME0MLY4CARB0HT1PS 

\ 

CARBONS  MADE  fft  THE 

NATIONAL  CAR80NC0.,CUEVELAND,0. 

ANO  PURCHASEWnDER  SPEC.17-C-Sro«36-SEARCH LIGHTS. 

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Fig.  5. 


20 


THE   SEARCHLIGHT. 


aAK 

No.  13. 

COMPARISON 

SPECTRUM  INTENSITIES 

^RC  ANO  RESULTANT  BEAMOF 

LOW  POWER  36  INCH  SEARCHLIGHT 

SHOWING 

COLOR  SELECTION 

ENERGYEFFICIENCY 
or 
ASSR4RAB0LIC  MIRROR«<i>FRONTLENS 

U5IM0 

PLAIN  CORE  POSITIVE 

MAKE  BV 

4TI0NAL  CARBON  C0.,CLEVEUNO,O. 
PURCHASEDUH0£RSPtC.I7-C-5 

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Color 
Fia.  0. 


THE   SEARCHLIGHT. 


21 


Plate 

No.l5. 

/ 

\ 

COMPARISON 
SPECTRUM  INTENSITYOFARC 

ANO 

RESULTANT  BEAM 

OF 

/ 

\ 

35.0 
32.5 

\ 

SPERRYH1GHP0WER36"SEARCHLI6HTARC 

SHOWING 

COLOR  SELECTION 

AND 

ENERGY  EFFICIENCY 

OF 

GLASS  PARABOLIC  MIRRORSahdFRONT  LENS 

/ 

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V . 

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CARBONS  MADE  BY 

27.5 

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Ul 

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UJ   .?•)  e 

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V                  CURVE  B  SHOWS  SPECTRUM  INTENSITVOFBEAM 

• 

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1      Yellow       |  Ohanqe  j 


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Fic; 


22 


THE   SEARCHLIGHT. 


comparison 
spectrumTntensity 

BEAMS  OF  HIGH  &  LOVI  POWER  36  INC  H 

NAVAL  SEARCHLIGHTS 
Curve  A-  beam  ofsperrymigm  power  spircmlioht 

CURVE  B-  BEAM  OF  NAVY  STANDARD  LOW  POWER 

SEARCnUGHTUSlNO  HARD  CORE  WrtlTff  LAME 

POSITIVE  BURNINOON  IIOAMP 
CURVE  C-BEAM  Of  NAVY  STANDARD  LOW  POWER 

SEARCHLIGHT  USING  PUIN  POSITIVE  C  ARBON 

BURNINOON  IIOAMP. 
CURVE  0-BEAM OF  BECK  SEARCHLIGHTU&ING  CARBONS 

MADEBYG  E.CO 


Violet    jP  j       Bi-ue      | 


Wavelength 

YcuLOw         [OaAHOE I 


Color 
KiG.  8. 


THE  SEAKCHUGHT. 


23 


??J0 
21.75 
2000 
/fl.75 

Plate 

No.16* 

COMPARISON 

or 
SPECTRUM  INTENSITIES ofARC 

AND 

RESULTANT  BEAM 
OF 
LOW  POWER  36"  SEARCHLIOHTS 

SHOWING 

COLOR  SELECTIONS 

AND 

ENERGY  EFFICIENCY 

OF 

GLASS  PARABOLICMIRROR&FRONTLEMS 

USING  WHITE  FLAME  HARDCORE  POSITIVE 

MADE  BY 

THENATIONALCARBONCO..aEVtUlH0.0 

/ 

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CURVE  B  snows  SPECTRUM  IMTENSITV  Of  BEAM 

i 

/ 

V 

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Violet  |P  I        Blue       | 


Wave Length , 
Yellow    |  Orange  | 


Color 

Fig.  9. 


CHAPTER  3. 
BECK  36  AND  30  INCH  HIGH-POWER  SEARCHLIGHTS. 


Tlie  Beck  light  does  not  difTer  materially  in  external  appearance  from 
the  older  t3-pe  of  searchlight,  the  arrangement  of  the  arc  with  respect  to  the 
mirror  being  similar  to  the  arrangement  in  previous  lamps.  Tlie  great  differ- 
ence occurs  in  the  source  of  light.  Smaller  carbons  and  greater  current  densi- 
ties are  employed  than  in  the  low-powered  searchlights  hitherto  in  use;  more- 
over, the  positive  carbon  has  a  core  of  light-emitting  substances,  the  composition 
of  which  is  known  onl}'  to  the  manufacturers. 

Another  noteworthy  feature  of  the  Beck  lamp  is  the  method  of  keeping 
the  carbons  cool  by  surrounding  them  with  an  alcohol  flame.  ITie  alcohol 
flame  is  a  reducing  medium  and  prevents  oxidation  of  carbons  back  of  tips, 
thereby  preventing  the  heat  of  this  additional  burning.  Also,  the  carbons  do 
not  ''spindle"  and  the  cross  section  is  constant,  therefore  no  additional  heat 
is  developed  by  PK  loss  increasing,  as  it  would  with  constant  current  and 
smaller  area  of  conductor.  The  alcohol  feature,  however,  is  objectionable 
because  it  prevents  the  light  being  used  for  anti-aircraft  purposes  to  any  great 
extent  unless  extra  mirrors  are  used  in  front  of  searchlight.  (These  mirrors 
are  inclined  45°  to  the  horizontal  and  deflect  the  beam  vertically  upward.) 
After  the  lamp  is  tilted  upward  to  a  certain  angle  the  alcohol  ceases  to  flow, 
and  the  carbon  "cooling"  system  is  therefore  out  of  service  for  as  long  as  the 
light  is  elevated  beyond  this  angle,  absolutely  unfitting  the  lamp  for  being  used 
to  search  the  zenith  or  any  at  very  high  angles. 

This  searchlight  is  excellent  for  use  where  high-angle  searching  is  not 
rerjuircd  and  is  far  superior  to  the  old  type  of  pure  carbon  arc  searchlight. 

The  following  is  a  reproduction  of  parts  of  the  instruction  book  on  Beck 

searchlights  furnished  by  the  General  Electric  Co.     From  it  may  be  obtained 

an  idea  of  the  operation  of  the  lamp.     Further  information  may  be  obtained 

from  the  report  of  the  test  on  the  sample  44-inch  Beck  searchlight  supplied  to 

the  navy  yard.  New  York,  for  trial.     This  test  report  follows  extracts  from 

instruction  book. 

Small  Carbons. 

The  positive  carbon  has  a  special  core  and  develops  a  deep  crater  of  high  intrinsic  brilliancy 
and  small  diameter,  resulting  in  a  beam  of  high  intensity  and  very  small  dispersion.  The  posi- 
tive carbon  is  in  the  axis  of  the  searchlight  barrel  and  the  negative  carbon  is  inclined,  in  the  ver- 
tical plane,  to  the  positive. 

Rotation. 

To  prevent  an  uneven  burning,  due  to  the  rising  arc  stream,  both  carbons  are  rotated  by  a 

motor. 

Alcohol  Flame. 

An  alcohol  flame  envelops  both  carbons,  resulting  in  the  cooling  of  the  electrodes  and  the 
removal  of  combustible  gases  from  the  air  immediately  surrounding  the  burning  carbon  tips, 
thereby  reducing  the  burning  rate  of  the  carbons. 

24 


36  inch  High  Powered  Mechanical  Control  Searchlight 


FIG.   to— BECK    HIGH    POWER  SEARCHLIGHT.     RIGHT   SIDE. 


THE  SEAECHLIGHT. 
Arc  rating  and  carbon  dimensions. 


25 


Size  of 
lamp, 
inches. 

Amperes. 

Arc  volts. 

Positive. 

Negative. 

Diameter. 

Length. 

Diameter. 

Length. 

36 
30 

150 
120 

75 
72 

mm. 
16 
13 

mm. 
1,100 
1,000 

mm. 
11 
11 

mm. 
340 
270 

Descrxption. 


lulion. — This  Mixture  is  Poisonous  and  the  Warning  "Wood  Alcohol  Poison"  is 
JILLED  on  the  Side  of  the  Alcohol  Tank,  Part  1,  Figure  11. 

Table  of  specific  gravity . 

For  the  best  results,  a  mixture  of  methyl  (graiu)  and  ethyl  (wood)  alcohol  should  be  used.    Low  grades  of  alcohol 
/■  contain  an  excess  of  water  and  the  mixture  should  be  of  the  specific  gravity  shown  in  the  table.] 


Grade. 

Per  cent. 

Specific 
gravity 

at  fi0°  F. 

(15°  C). 

50 
.50 
100 

0.815 
.811 
.813 

Wood       ..                     

Tank. — The  alcohol  should  be  strained  through  a  chamois  skin  and  kept  in  clean  receptacles. 
In  fUUng  the  tank,  remove  the  cap,  part  2,  figure  10,  and  pour  the  alcohol  slowly  into  the  opening. 
In  entering  the  tank  the  alcohol  passes  through  a  200-mesh  wire  screen. 

Indicator. — In  one  end  of  the  tank  there  is  an  indicator,  part  3,  figure  12,  with  a  scale  marked 
in  pints.  This  indicator  is  of  the  magnetic  t>T)e  there  being  a  permanent  magnet  inside  the  tank 
attached  to  a  float.  The  movement  of  the  magnet,  caused  by  changes  in  the  level  of  the  alcohol, 
causing  a  corresponding  movement  of  the  pointer  on  the  outside  of  the  tank. 

Valves,  pipes,  filter,  and  vaporizer. — Directly  below  the  tank  is  the  shut  off  valve,  part  4, 
figure  11.  The  tank  is  connected  by  a  pipe,  part  9,  figure  11,  to  the  filter,  part  5,  figure  11,  in  which 
the  alcohol  passes  through  one  200-mesh  and  one  65-mesh  wire  screen.  From  the  filter  the  alcohol 
passes  through  an  opening  0.012  inch  diameter,  a  valve  and  a  coil  pipe  to  the  vaporizer  part  10, 
figures  13  and  16,  where  it  passes  through  four  thicknesses  of  32-mesh  wire  screen  to  the  inner  wall 
of  the  vaporizer.     A  heating  unit,  part  11,  figures  13  and  16  vaporizes  the  alcohol. 

At  the  aide  of  the  filter  is  a  push  rod,  part  7,  figure  11,  carrying  a  fine  wire  which  when  the 
rod  part  7  is  pushed  in  enters  the  small  filter  outlet  hole  and  clears  it  of  any  obstruction. 

Burners  and  Jlame. — The  vapor  passes  up  the  pipe,  part  12,  figures  13  and  16,  to  the  burners, 
parts  13  (positive)  and  14  (negative),  figures  13  and  16.  The  positive  burner  has  two  narrow, 
tapered  openings  which  divide  the  positive  flame,  causing  one  jet  to  pass  on  one  side  and  the  other 
on  the  opposite  side  of  the  carbon.  The  negative  burner  has  one  narrow  opening.  It  is  important 
that  these  openings  be  kept  free  from  dirt. 

Vent  screw. — Part  6,  figure  11,  is  a  vent  screw  which  should  be  opened  to  allow  trapped  air  in 
the  pipe,  part  9,  to  escape.  This  should  })e  left  open  until  the  alcohol  flows  through  the  vent. 
It  should  be  unnecessary  to  open  this  vent  except  in  case  of  leakage  in  the  pipe,  part  9,  or  the 
supply  of  alcohol  has  become  exhausted. 

THE   THERMOST.^T   AND    ABC   IMAfiE    SYSTE.M. 

The  image  of  the  crater  of  the  positive  carbon  is  focused  on  the  strips  of  the  thermostat,  part  32, 
figures  18  and  20,  Ijy  means  of  the  lens,  part  36.  and  the  muror.  part  37.  figure  21.  This  thermo- 
stat controls  a  feeding  magnet,  part  41,  figures  16  and  17,  which  in  tui-n  controls  the  positive  feed 
rod,  part  42,  figures  13  and  16. 


26  THE  SEAKCHUGHT. 

By  means  of  a  lens  mounted  in  a  tube  in  the  searchlight  barrel  and  projecting  into  the  thermo- 
stat box,  part  43,  figure  10,  the  image  of  the  arc  is  projected  on  a  mirror,  part  34,  figure  18,  and 
reflected  to  mirror,  part  33,  figure  18,  then  reflected  to  the  ground  glass,  part  35,  figure  18.  The 
image  of  the  arc  is  inverted  on  the  ground  glass.  Two  vertical  linee  on  the  ground  glass  mark 
the  correct  position  for  the  tips  of  the  carbons. 

ROTATION   OF  CAHBONS. 

Motor,  shafts,  gears,  and  rollers. — The  feeding  and  rotating  motor,  part  15,  figures  16  and  17, 
is  connected  by  gearing  to  the  positive  rotation  rod,  part  16,  figures  13  and  16,  and  the  negative 
rotation  rod,  part  17,  figures  13  and  16.  These  rods  have  at  their  upper  ends  bevel  gears,  parts 
18  and  19,  meshing  with  gears,  parts  20  and  21,  figure  10,  by  means  of  which  the  movable  portion 
of  the  carbon  head  is  rotated.  This  rotary  movement  is  transmitted  to  the  carbons  by  means  of 
the  spring- pressed  knife-edged  rollers,  parts  26  and  28,  figure  16. 

Contacts. — Supported  on  the  stationary  part  of  the  carlion  heads  are  contact  arms,  parts  46 
and  47,  figure  16,  fitted  with  flexible  silver  connection  strips,  parts  48  and  49,  and  silver  contact 
blocks,  parts  50  and  51,  having  concave  contact  surfaces  pressed  against  the  carbons  by  the  weight 
arms,  parts  22  and  23,  figure  16. 

Guiding  of  carbons. — The  carbons  are  guided  by  the  bore  in  the  carbon  head  nosee,  parts  24 
arid  25,  figure  16,  and  by  the  rollers,  parts  26,  27,  28,  29,  figure  16. 

FEEDING   OF  CARBONS. 

Gearing  and  ratchets. — In  the  revolving  mechanism  of  each  carbon  head  is  a  star  wheel  con- 
nected by  a  worm  and  a  worm  wheel  to  the  shaft  carrying  the  knurled  faced  feeding  rollers,  parts 

27  and  29,  figure  16. 

The  negative  feed. — The  negative  feed  is  set  by  hand  by  means  of  the  lever,  part  30,  figures 
15  and  16,  moving  over  a  notched  and  graduated  dial,  part  52,  and  connected  to  the  cam,  part  52, 
figure  16.  which  raises  or  lowers  the  feed  rod,  part  32,  figures  13  and  16.  The  upper  end  of  this  rod 
engages  the  star  wheel  at  the  lower  point  of  the  path  of  its  rotation  around  the  axis  of  the  carbon, 
rotating  the  star  wheel  through  a  few  degrees  or  several  degrees  depending  on  the  setting  of  the  arm, 
part  30,  thus  increasing  or  diminishing  the  rate  of  feed  of  the  carbon. 

The  positive  feed — Thermostatic  regulation. — When  the  positive  carljon  tip  is  on  its  line  on  the 
screen,  part  35,  figure  18,  the  crater  image  is  on  the  edge  of  the  first  thermostat  strip,  part  32, 
figures  18  and  20.  As  the  carbon  bums  away,  the  crater  image  is  reflected  further  onto  the  first 
thermostat  strip  deflecting  it  and  closing  the  contacts,  parts  53  and  54,  figures  17  and  20,  com- 
pleting the  circuit  to  the  feeding  magnet,  part  41,  figures  16  and  17.  The  feeding  magnet  armature 
in  closing  raises  the  positive  feed  rod,  part  42.  figure  13  and  16.  bringing  it  into  the  path  of  the 
rotating  ratchet  connected  to  the  feeding  rollers  and  feeding  the  carbon  ahead.  This  advance 
of  the  carbon  occurs  during  each  revolution  of  the  carbon  head  until  the  positive  carbon  tip  is 
again  in  the  exact  focus  of  the  mirror  and  the  crater  image  has  moved  to  the  edge  of  the  thermostat 
strip  opening  the  circuit  to  the  feeding  magnet  which,  in  turn,  lowers  the  feeding  rod  and  stops 
the  feeding. 

Hand  regulation. — If  the  thermostatic  regulation  becomes  inoperative,  it  is  cut  out  of  the 
circuit  by  opening  the  switch,  part  55,  figures  10  and  18.  The  hand  feed  is  then  operated  in  the 
same  manner  as  the  negative  feed. 

Emergency  quick  feed. — For  the  purpose  of  moving  the  carbon  rapidly  forward  the  positive 
feed  lover,  part  41,  figures  14  and  Ifi,  may  be  moved  to  the  extreme  left-hand  end  of  the  dial,  part 
45,  figure  14,  against  a  stop.  This  lowers  the  quick  feed  rod,  part  43,  figures  13  and  16,  and  raises 
the  latch,  part  56,  figures  13  and  16,  locldng  the  internal  gear,  part  57,  figure  16,  which,  through  a 
pinion  rapidly  revolves  the  worm  shaft  geared  to  the  feed  rollers,  and  the  carbon  is  fed  ahead  at  a 
rapid  rate. 

THE    STARTING    MOTOR. 

A  starting  motor,  part  58,  figure  16,  is  connected  by  gears,  sprockets,  and  chain  with  the  nut, 
part  69,  figure  16,  engaging  with  the  screw,  part  60.  The  rotation  of  this  nut  causes  the  screw  to 
move  forward  or  back.    The  screw  is  attached  to  the  negative  carbon  carriage. 

HAND   START. 

The  lamp  may  be  started  by  hand,  using  the  handwheel,  part  61,  figures  15  and  16. 


FIG.    11.      BECK    HIGH    POWER    SEARCHLIGHT.       LEFT   SIDE. 


FIG.    12.— BECK    HIGH    POWER   SEARCHLIGHT,     BACK   VIEW. 


THE  SEABCHUGHT.  27 


VENTILATION. 

A  fan,  direct  connected  to  a  motor,  is  mounted  in  the  top  of  the  barrel  and  exhausts  through 
the  opening,  part  69,  figure  12.    This  fan  removes  the  gases  from  the  arc  and  cools  the  mirror. 

LIMrr   SWITCH. 

The  limit  switch,  part  62,  figures  16  and  19,  consists  of  a  base  sliding  on  guide  rods  and  held 
in  position  by  a  spring.  It  carries  insulated  contacts  and  contact  arms  and  is  operated  by  an 
insulated  stud  on  the  negative  carbon  carriage. 

The  functions  of  this  switch  are  as  follows: 

First.  In  connection  with  the  reversing  relay,  to  connect  the  starting  motor  as  a  series 
motor  in  advancing  the  negative  carbon  carriage. 

Second.  To  limit  the  forward  motion  of  the  negative  carbon  carriage  in  case  the  carbons  fail 
to  meet  due  to  the  carbons  being  improperly  adjusted  or  breakage  of  either  carbon. 

Third.  In  connection  with  the  reversing  relay,  to  reverse  the  starting  motor  in  striking  the  arc. 

Fourth.  To  open  circuit  and  apply  a  dynamic  brake  to  the  armature  of  the  starting  motor 
when  the  arc  has  been  established. 

The  limit  switch  may  be  moved  along  the  guide  rods  by  the  push  rod,  part  63,  figures  15  and 
19,  to  produce  an  arc  shorter  than  normal. 

CONNECTIONS   OF  LAMP. 

Refer  to  figure  17.  The  rheostat  is  in  series  with  the  lamp  and  is  connected  in  the  negative 
side  of  the  circuit.  The  negative  potential  wire  A,  the  main  negative  lead  B,  and  the  main 
positive  lead  C  are  brought  to  the  lamp  through  contact  rings  and  plungers  in  the  base  and  on  the 
turntable  of  the  projector.  The  main  leads  B  and  C  are  connected  to  the  insulated  carbon  sup- 
ports through  flexible  connection  strips. 

The  series  wound  ventilating  motor  part  64  and  the  heating  unit,  part  11,  of  the  vaporizer 
are  connected  directly  across  the  positive  lead  C  and  the  negative  potential  wire  A  so  that  they 
receive  the  full  Une  voltage.  The  feeding  and  rotating  motor,  part  15,  has  its  field  connected 
between  the  main  negative  lead  B  and  the  negative  potential  lead  A,  and  its  armature  connected 
through  the  switch,  part  66,  figure  18,  to  the  same  source.  This  connection  is  essentially  across 
the  rheostat  and  the  motor  operates  only  when  the  lamp  is  burning  and  current  is  passing  through 
the  rheostat. 

The  relay,  part  67,  figure  16,  is  also  connected  between  the  main  negative  lead  B  and  the 
negative  potential  lead  A,  or  across  the  rheostat,  and  closes  when  current  passes  through  the 
rheostat. 

The  feeding  magnet,  part  41,  is  connected  on  one  side  to  the  negative  potential  lead  A  and  on 
the  other  side,  through  the  contacts  of  the  thermostat,  and  the  thermostat  switch,  part  55,  to  the 
main  positive  lead  C.     Part  68  is  a  discharge  resistance  for  the  feeding  magnet. 

The  starting  motor,  part  58,  has  a  series  and  a  shunt  field  with  a  switch,  part  70,  in  the  armatiu'e 
circuit.  With  the  limit  switch,  part  62,  and  the  relay,  part  67,  in  the  starting  positions,  the  starting 
motor  is  connected  as  a  series  motor  across  the  line  or  between  the  main  positive  lead  C  and  the 
negative  potential  lead  ,\  and  advances  the  negative  carbon  carriage  until  the  carbons  touch. 

With  the  limit  switch  part  62  and  the  relay  part  67,  in  the  running  position,  the  motor  is 
reversed  and  operates  as  a  shunt  motor  separating  the  carbons  until  the  arc  has  been  drawn  out 
to  the  proper  length,  when  the  motor  is  stopped  by  the  limit  switch  part  62  opening  the  circuit. 

Operation. 

inserting  carbons. 

If  partially  burned  carbons  are  to  be  used,  see  that  the  end  of  the  positive  carbon  is  cut  off 
squarely,  using  the  carbon  cutters  furnished  in  the  tool  box. 

Rotate  the  negative  carriage  by  means  of  the  handle  part  65,  figures  13  and  16,  until  the 
carriage  strikes  a  stop.  Separate  the  carbon  head  rollers  by  rotating  the  negative  releasing  handle 
part  71,  figures  15  and  16,  and  the  positive  handle  part  72,  figures  13  and  16,  counterclockwise 
facing  the  ends  of  the  lamp.    This  separates  the  feeding  and  rotation  rollers. 

On  account  of  the  ratchet  in  the  hand  rotation  mechanism,  it  is  necessary  to  grasp  both  the 
positive  and  the  negative  releasing  handles  at  the  same  time,  as  rotation  of  either  positive  or  nega- 


28  THE  SEARCHLIGHT. 

tive  releasing  handle  without  locking  the  other  drives  back  through  the  gearing  and  rotates  the 
other  carbon  head. 

Raise  the  contact  arm  weights  parts  22  and  23,  figures  13  and  IG,  and  insert  the  negative 
carbon  from  the  front  of  the  negative  head.  Insert  the  positive  carbon  through  the  carbon  tube 
part  "3,  figures  10  and  11. 

Rotate  the  negative  carriage  back  to  its  running  position  and  adjust  the  carbons  so  that  the 
negative  projects  1%  inches  and  the  positive  projects  l^  inches  from  the  ends  of  the  noses,  as 
shown  in  figure  16.  Lower  the  contact  arm  weights  and  rotate  the  releasing  handles  clockwise 
back  to  their  former  positions.    This  causes  the  rotating  and  feeding  rollers  to  grip  the  carbons. 


Contumption  of  alcohol. — Note  the  position  of  the  alcohol  indicator  and  make  sure  there  is  a 
supply  of  alcohol  sufficient  for  the  run.    The  conauraption  of  alcohol  is  1.5  pints  per  hour. 

Setting  negative  support. — Pull  the  hand  starting  hand  wheel  part  61,  figure  15,  outward  and 
rotate  in  a  clockwise  direction,  facing  the  handwheel  until  the  negative  carriage  strikes  a  stop; 
then  rotate  counterclockwise  2^  turns.  Push  the  handwheel  in  throwing  it  out  of  engagement 
with  the  starting  gearing.    The  carbons  should  now  be  J  inch  apart. 

Vaporization. — Open  the  main  alcohol  valve  part  4,  figure  11.  Close  the  main  switch  in  the 
projector  base.  This  will  .start  the  ventilating  motor  and  complete  the  circuit  through  the 
vaporizer  heating  unit.  Allow  from  one  and  one-half  to  two  minutes  for  the  vaporizer  to  become 
hot,  then  open  the  alcohol  valve  in  the  base  of  the  lamp  by  turning  the  knob  part  7-1,  figures  12, 
15,  and  16.     Apply  a  match  to  the  burners  and  observe  the  height  of  the  alcohol  flames. 

Height  of  flame. — The  positive  should  be  12  inches  and  the  negative  10  inches  high.  The 
vapor  will  ignite  from  the  arc,  but  it  is  better  to  light  the  flame  before  starting,  so  that  the  height 
of  the  flames  may  be  noted.  If  the  flames  are  not  the  proper  height,  push  in  the  rod  part  7,  figure 
11,  once  or  twice.     See  that  the  thermostat  switch  part  55,  figure  10,  is  closed. 

Starting  stifitch. — Close  the  starting  switch  part  70,  figures  15  and  16.  This  will  start  the  lamp. 
If  the  arc  drops  repeatedly  owing  to  the  absence  of  a  crater  in  a  new  positive  carbon,  push  in  the 
rod  part  63,  figures  15  and  19  and  hold  until  a  crater  is  formed. 

RUNNING. 

Adjustment  of  feed. — Observe  the  image  of  the  burning  carbons  on  the  screen  part  35,  figure 
18.  The  tips  should  touch  the  vertical  lines  on  the  screen.  Adjust  the  lever  part  30,  figures 
15  and  Ifi,  until  the  rate  of  feed  is  such  that  the  negative  carbon  tip  holds  to  its  line  on  the  screen. 
If  the  negative  carbon  tip  is  to  the  right  of  this  line  the  arc  is  too  long  and  the  lever  should  be 
moved  a  small  amount  to  the  right.  This  increase.^  the  rate  of  feed.  If  the  negative  carbon  tip 
is  to  the  left  of  this  line  (between  the  negative  and  positive  lines),  the  arc  is  too  short  and  the 
feed  too  rapid.  Move  the  lever  to  the  left  a  small  amount.  Repeat  tliis  operation  until  the  rate 
of  feed  is  equal  to  the  carbon  consumption  and  the  negative  carbon  tip  holds  to  its  line.  This 
adjustment  will  need  very  little  change  during  a  run.  Variation  in  the  burning  rate  of  different 
carbons  will  make  a  slight  change  in  adjustment  necessary  from  time  to  time. 

The  lever  part  44,  figures  14  and  16,  should  be  sot  at  zero.  If  the  image  of  the  positive  ciubon 
is  to  the  left  of  its  line,  the  arc  is  beyond  the  focus  of  the  mirror.  Turn  the  adjusting  knob 
part  75,  figures  10  and  20,  a  slight  amount  in  the  direction  marked  ''Back."  If  the  image  ia  to 
the  right  of  the  line  (between  the  lines),  turn  the  knob  slightly  in  the  other  direction.  This 
adjustment  must  be  made  whenever  a  change  in  the  temperature  of  the  air  in  the  thermostat 
box  affects  the  curvature  of  the  thermostat  strips,  part  32.  In  case  the  thermostatic  regulation 
is  inoperative,  place  the  switch  part  55  in  the  off  position.  The  lever  part  44  must  then  be  adjusted 
to  hold  the  positive  carbon  on  its  line,  as  described  above  for  the  negative  carbon. 

Stopping  carbon  rotation.— li  the  positive  carbon  starts  to  burn  irregularly,  stop  the  rotation 
of  the  carbons  by  opening  the  switch  patt  66,  figure  18,  when  the  projection  is  uppermost  (at  the 
lowest  point  on  the  screen  part  35),  allowing  the  rising  flame  to  burn  it  off.  Then  close  the  switch, 
allowing  the  carbons  to  resume  rotation. 

Quirk  feed.— In  case  the  positive  carbon  should  be  burning  some  distance  back  of  its  line  or 
if  it  becomes  broken,  move  the  lever  part  44  to  the  left  against  the  stop  and  hold  until  the  carbon 
is  fed  up  to  its  line. 


36  inch  High  Powered  5edrch//ght  Lamp 


FIG.    13.— BECK    HIGH    POWER    SEARCHLIGHT    LAMP.      RIGHT    SIDE. 


FIG.  U.-BECK   HIGH   POWER  SEARCHLIGHT   LAMP.     THREE-QUARTER  FRONT  VIEW. 


THE  SEARCHLIGHT.  29 

In  case  enough  of  the  carbon  is  broken  off  to  cause  the  arc  to  drop,  the  rotation  motor  will  stop. 
Open  the  starting  switch  part  70,  figure  15,  return  the  negative  carriage  to  the  starting  position 
by  means  of  the  hand  starting  handwheel,  part  61,  figure  15.  Hold  the  positive  feed  lever  part 
44,  figure  14,  to  the  extreme  left  of  the  dial,  insert  the  hand  rotation  wrench  in  the  opening  in 
the  side  of  the  lamp,  rotating  the  wrench  counterlockwise  until  the  positive  carbon  tip  is  again 
on  its  line.  This  can  be  seen  by  aid  of  the  alcohol  flame.  Release  the  positive  feed  lever  and 
close  the  starting  switch. 

ShoTl-arc  pxtsh  rod. — If  the  arc  drops,  due  to  air  blast  from  gun  fire,  push  in  the  rod,  part  63, 
figure  15,  and  at  the  same  time  rotate  the  hand  start  wheel,  part  61,  figure  15,  counterclock^vise 
to  shorten  the  arc.  The  rod  part  63,  figure  15,  should  be  held  in  as  long  as  the  short-arc  condi- 
tion is  required. 

Hand  feed  and  rotation  of  carbons. — If  the  feeding  and  rotating  motor  fails  to  operate  insert 
the  hand  feed  wrench  through  the  opening  in  the  side  of  the  lamp  and  rotate  counterclockwise 
about  50  revolutions  per  minute.  Hand  rotation  should  start  as  soon  as  the  arc  strikes  and  must  be 
continuous.  If  the  positive  carbon  burns  irregularly  the  hand  rotation  must  be  stopped  when 
the  projecting  lip  of  the  carbon  is  uppermost  until  the  lip  is  burned  off. 

STOPPING. 

Open  the  main  switch  in  the  searchlight. 

Open  the  starting  switch,  part  70,  figure  15. 

Close  the  valves,  parts  4  and  74,  figure  12. 

Observe  alcohol  supply  for  the  next  run. 

Remove  the  dust  from  the  mirror  and  front  door  strips. 

A  duster  is  furnished  in  the  tool  box  for  this  purpose. 

CAHE    OP   L.VMP. 

Keep  the  lamp  clean,  remo^-ing  all  carbon  du.st  after  each  run. 

Note  paiis  marked  oil  and  grease,  on  figure  16,  and  keep  oil  and  grease  cups  full.  Use  a  good 
grade  of  light  machine  oil  and  a  light  grease  or  mixture  of  grease  and  graphite  for  the  grease  cups. 
Apply  only  a  small  amount  of  oil  through  the  oil  hole  each  time,  wiping  away  any  excess. 

The  switch,  relay,  thermostat,  limit  switch,  and  other  connections  should  be  kept  clean. 
Use  fine  sandpaper  in  cleaning  contacts,     do  not  use  emery  cloth  or  paper. 

The  carbon  contacts,  parts  50  and  51,  figure  16,  should  be  inspected  frequently  and  kept  clean. 
The  curvatures  of  the  contact  surfaces  must  be  kept  in  their  original  forms  to  correspond  with 
the  curvature  of  the  carbons. 

The  brushes  of  the  rotating,  starting,  and  ventilating  motors  should  be  kept  clean  by  occa- 
sionally sandpapering. 

Lenses  and  mirrors  in  the  thermostat  box  should  be  kept  clean  and  free  from  dust.  In  clean- 
ing care  should  be  taken  not  to  disturb  the  adjustment  of  the  mirrors. 

Carbon  heads  should  be  reamed  out  occasionally,  with  reamers  furnished  in  the  tool  box,  to 
remove  accumulations  of  carbon  dust  or  scale. 

ADJUSTMENTS. 

Focusing. — In  previous  searchlights  not  using  the  high  powered  lamp,  focusing  was  accom- 
plished by  moving  the  entire  lamp  toward  or  from  the  mirror.  In  the  high-powered  searchlights 
the  lamp  is  fixed  in  the  drum,  with  respect  to  the  parabolic  mirror  and  the  essential  condition 
which  must  be  maintained  is  the  projection  of  the  positive  carbon  1-^  inches  from  the  end  of  the 
carbon  head. 

A  positive  carbon  carriage  adjusting  screw,  part  77,  figure  16,  and  a  nut,  part  78,  figure  14 
and  16,  provide  means  of  moving  the  carriage  toward  or  from  the  mirror,  with  the  lamp  in  its  fixed 
position,  but  should  only  be  used  when  adjusting  the  lamp  to  a  new  parabolic  mirror  having  a 
different  focal  length  than  the  mirror  with  which  the  lamp  was  adjusted,  or  in  replacing  the  lamp 
with  a  spare  lamp. 

Replacing  mirror. — Proceed  as  follows: 

First.  Open  the  thermostat  switch,  part  55,  figure  10,  and  set  carbons  as  shown  in  figure  16. 

Second.  Start  the  lamp,  observe  the  beam  and  if  the  rays  cross  (hourglass  in  shape)  move  the 
nut,  part  78,  figure  14,  counterclockwise.  If  the  beam  spreads  move  the  nut,  part  78,  clockwise 
until  the  beam,  when  thrown  on  a  distant  object,  is  as  small  in  diameter  as  it  is  possible  to  obtain. 


30 


THE   SEARCHLIGHT. 


\Vhenever  the  positive  carbon  carriage  is  moved  by  the  nut,  part  78.  figure  14,  it  is  necessary 
to  adjust  the  push  rod,  part  63,  figure  15,  by  removing  the  lamp  side  cover  and  loosening  the  set 
screw  at  point  marked  86,  figure  19,  and  turning  the  rod,  part  63,  until  it  can  be  pushed  in  -ff  inch. 

Third.  Stop  the  lamp,  readjust  the  carbons  and  repeat  adjustment  No.  2,  until  the  proper 
beam  is  obtained  with  the  positive  carbon  projecting  IfJ  inches. 

Fourth.  Adjust  the  thermostat  mirror,  part  37,  figure  18,  until  the  image  of  the  crater  is  ^  inch 
on  the  first  thermostat  strip,  part  79,  figure  20.  The  arc  image  should  be  in  the  center  of  the 
thermostat  strip,  vertically.  This  mirror  is  adjustable  in  two  planes  by  means  of  the  screws, 
parts  80  and  81,  figure  18. 

Fifth.  Close  thermostat  switch. 


Fia.  16. — Beck  high-power  searchlight  lamp.    Sectional  assembly. 

Sixth.  Adjust  the  arc-image  mirror,  part  34,  figure  18,  until  the  image  of  the  positive  carbon 
tip  is  on  its  line  on  the  screen,  part  35. 

Installing  spare  lamp. — The  thermostat  and  arc-image  mirrors  having  been  properly  set  for  the 
mirror  which  is  in  the  projector  require  no  adjustment. 

First.  Set  the  carbons  as  shown  in  figure  16  and  start  the  lamp. 

Second.  Rotate  the  nut,  part  78,  figure  14,  until  the  tip  of  the  positive  carbon  is  on  its  line 
on  the  screen,  part  35. 

•Third.  Check  the  length  of  the  positive  carbon  beyond  the  carbon  head.  This  should  be 
l-fi  inches.    If  not  correct  reset  and  repeat  adjustment  No.  2. 

Arc-image  and  thermostat  mirrors.  If  the  adjustment  of  the  arc-image  or  thermostat  mirrors 
has  become  accidentally  changed,  adjust  the  arc  image  mirror  by  use  of  the  adjusting  screws  until 
the  im^e  of  the  positive  carbon  tip  is  on  its  line  on  the  screen,  part  35,  noting  carefully  that  the 


TSB  SEAKCHLIGHT. 


31 


positive  carbon  is  in  focus  and  projects  lyj  inches  from  the  head.    Adjust  the  thermostat  mirror 
aa  described  in  the  fourth  adjustment  under  replacing  mirror. 

Thermostat  co/'i(ac(5. ^Referring  to  figure  20,  the  pivot  point,  part  82  should  be  so  set  that 
there  is  0.001  inch  between  the  point  and  the  thermostat  strip. 


(WWW- 


64 


o 


63 


o 


S^.- 


Fig.  17.— Beck  high-power  searchlight.    Wiring  diagram. 

'  "The  screws,  part  53,  figure  20,  should  be  adjusted  so  that  they  are  the  same  distance  from 
the  contacts,  part  54. 

"f  IFeed  rods. — When  the  levers,  parts  30  and  44,  are  set  at  zero  there  should  be  ^  inch  between 
the  upper  ends  of  the  feed  rods,  parts  32  and  52,  figure  13,  and  the  points  of  the  star-wheel  teeth 
when  the  star  wheel  passes  the  feed  rod. 

Burners. — If  burners  are  replaced  they  should  be  adjusted  exactly  as  shown  in  figure  16. 


32 


THE  SEABCHLIGHT. 


Carbon  head  springs. — If  the  tension  springs  on  the  feed  rollers  are  replaced  the  new  springs 
should  be  adjusted  so  that  the  rotation  and  feed  rollers  mark  faint  lines  of  the  carbons.  A  splinter- 
ing of  the  carbons  indicates  that  the  springs  are  too  tight. 

Carbon  support  guide. — If  it  becomes  necessary  to  move  the  carbon  supports  to  bring  the 
carbons  into  the  vertical  plane  of  the  axis  of  the  mirror,  adjust  the  guide,  part  87,  figure  19,  by 


Fio.  18.— Beck  Wgh-powcr  searchlight  l&mp.    Thermostat  and  arc  Image  system. 

the  screws,  part  12,  being  careful  to  put  no  strain  on  the  guide  by  unequal  movements  of  the 
adjusting  screws. 

Limit  switch. — In  case  it  is  necessary  to  replace  limit  switch  contacts  or  the  contact  springs 
have  become  distorted,  set  the  carbons  as  in  figure  16  and  back  off  the  small  set  screw  at  88,  figure  19. 


FIG.    15— BECK    HIGH    POWER    SEARCHLIGHT    LAMP,    SHOWING    CARRYING    BARS    IN    PLACE.     THREE- 
QUARTER    BACK    VIEW. 


THE  SEAECHUGHT. 


33 


Then  push  ia  the  rod.  jiart  i;:i,  and  rotate  the  rod  opposite  the  push  rod  until  contact  84  just  touches 
contact  83. 

All  of  the  above  adjustments  are  carefully  made  at  the  factory  and  should  not  be  changed 
unless  uecesaar>'. 


66- 


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.^'.'.W',^^■.^^^^-.k^'.^'.>.^k■.^^^^'.UA^^A.A.A^^..^^^^J'l 


Fig.  19. — Beck  high-power  searchlight  lamp.    Sectional  views. 
66438—18 3 


34 


THE   SEARCHLIGHT. 


Fio.  ao.— Beok  high-power  searchlight  lamp.    Arc  length  regulator  and  thermostat. 


THE   SEAECHUGHT. 


35 


Fio.  21  .—Beck  high-power  searchlight  lamp.    Relay  and  starting  switch. 


Report  ok  Tests  on  Beck  Searchliobt. 
[August,  1914.] 

1.  Tests  have  been  conducted  on  the  searchlight  submitted  by  Mr.  H.  Beck,  of  Meiningen, 
Germany,  through  his  representative,  Mr.  Auerbacher,  of  New  York  City,  to  determine  tlic  s\:it- 
ability  for  use  on  shipboard  as  compared  with  the  apparatus  now  in  use.  Tlie  searchlight  appara- 
tus consists  of  the  searchlight  and  rheostat. 

2.  Tlie  mechanical  construction  of  the  searchlight  is  as  follow:  The  metal  searchlight  drum 
is  suspended  in  two  bearing.-!,  the  pede.stals  of  which  are  fa^teued  by  bolts  to  the  top  of  a  hea\  y 
ca^t-iron  ciniilar  base.  Tliis  base  (its  over  an  iron  housing  used  as  the  base  of  the  searchlight. 
In  the  drum  of  the  searchlight  Ls  placed  the  light  projector.  In  the  back  of  the  drum  is  fastened 
by  meaiw  of  clutches  the  searchlight  dome  and  the  parabolic  glass  mirror.  On  the  front  of  the 
drum  is  placed  the  front-door  strips.  These  strips  are  placed  in  an  iron  flat  ring  and  this  ring  is 
suspended  on  two  sets  of  iron  grooved  rollers  placed  180°  apart  which  re.st  on  two  tracks  lastened 
to  the  drum.  On  either  side  of  this  iron  ring  are  placed  springs,  the  function  of  which  is  to  act 
as  a  cu-hion.  This  arrangement  is  used  to  minimize  the  shock  of  the  front-door  strips  (hie  to  gun 
fire  and  prevent  breakage.  .\n  iris  shutter  arrangement  is  placed  in  front  of  thc^e  gla.ss  strips  and 
the  opening  and  clo.^ing  of  the  .shutter  is  manipulated  by  means  of  the  turning  of  a  haiidwheel 
placed  on  the  side  of  the  searchlight  drum.  .V  small  iron  tube  used  to  protect  the  positive  carbon 
projects  from  the  front  side  of  the  searchlight.  On  top  of  the  drum  is  a  protected  opening  which 
permits  the  proper  dissipation  of  heat  radiated  from  the  arc.  There  is  also  placed  on  top  of  the 
drum  a  ventilating  fan  which  exhausts  all  the  gases  and  smoke  given  off  from  the  arc  and  the 
burning  alcohol  gas.  On  one  side  of  the  drum  is  a  square  opening  having  an  iron  hinge  cover. 
This  opening  permits  an  easy  access  to  any  part  on  the  inside  of  the  housing,  mirror,  or  lamp. 
On  this  side  also  is  fastened  a  small  5  liter  capacity  tank  used  for  storage  of  alcohol  used  in  con- 
nection with  the  burning  of  the  lamp.  .Vttached  to  this  tank  is  a  flexible  brass  protected  rubber 
tube  which  conveys  the  alcohol  to  the  lower  side  of  the  searchlight  projector.  On  the  bottom  of 
the  drum  is  fastened  a  ratchet  device  operated  by  a  handwheel  for  elevating  the  drum.  On  the 
other  side  of  the  drum  is  a  square  ground  glass  used  for  the  indication  of  the  position  of  the  arc 
with  respect  to  the  focal  center  of  the  mirror  and  also  to  observe  the  jirojjer  burning  of  the  arc. 
On  the  same  side  is  also  fastened  a  long  metal  box  containing  the  electrical  mechanism  by  means 
of  which  the  positive  carbon  is  kept  in  a  constant  position.  On  the  same  side  is  also  placed  a 
small  ratched  arrangement  operated  by  means  of  a  small  handwheel,  by  means  of  which  the 
searchlight  lamp  can  be  moved  backward  and  forward  in  the  drum.  The  drum  with  the  pedestal 
can  be  trained  in  azimuth  in  either  direction  and  the  amount  of  turning  is  indicated  by  a  scale 
fastened  on  the  base.     The  mechanical  construction  of  the  lamp  is  as  follows: 

The  lamp  consists  of  a  rectangular  housing  in  which  is  placed  the  motor  with  mechanical 
arrangements  for  feeding  the  carbons  together  and  apart  on  initial  striking  of  the  arc.  Another 
motor  with  mechanical  arrangements  is  placed  in  this  housing  for  the  purpose  of  rotating  the  car- 
bons. The  housing  also  contains  a  vaporizer,  superheater,  and  feed  regulator  for  the  alcohol. 
The  mj^net  controlling  the  operation  of  the  position  of  the  positive  controlling  rod  is  also  located 
in  this  housing.  On  top  of  the  lamp  housing  are  placed  the  carbon  holder  pedestals.  The  positive 
carbon  holder  pedestal  is  securely  fastened  to  the  lamp  housing  and  remains  in  a  fixed  position. 
The  negative  carbon  holder  pedestal  is  clamped  by  moans  of  screws  to  the  lamp  housing.  By  loosen- 
ing the  screws  the  negative  carbon  holder  pedestal  can  be  given  a  small  turn  and  the  negative  carbon 
can  he  easily  replaced  by  a  new  one.  On  top  of  each  pedestal  is  placed  the  carbon  holder.  The 
positive  carljon  holder  is  in  a  horizontal  position  and  the  negative  holder  is  placed  at  an  angle  of  14° 
with  the  horizontal  plane.  Each  carbon  holder  consists  of  two  parts,  the  stationarj'  |)art  used  as  a 
guide  for  the  rotating  carbons.  This  section  also  contains  the  current  contact  round  shoes  which 
are  made  of  silver.  The  other  part  of  the  carbon  holder  is  a  rotating  clamp  arrangement  for  clamp- 
ing and  rotating  the  carbons.     This  arrangement  rotates  constantly  and  causes  the  carbons  to 

36 


38  THE   SEARCHLIGHT. 

rotate  with  it.  The  rotation  is  accomplished  by  means  of  a  mechanical  arrangement  connected 
with  the  motor  used  for  that  purpose  in  the  lamp  housing.  The  clam])ing  arrang(>ment  is  com- 
posed of  two  rollers  so  adapted  as  to  effect  a  simultaneous  advance  of  the  carl)ons  while  rotating. 
The  speed  of  feeding  of  the  carbons  is  controlled  by  means  of  control  rods  located  alongside  of  the 
carbon  holder  pedestals.  \Mien  these  control  rods  are  raised  they  come  in  contact  with  a  little 
10-tooth  star  wheel  which  in  turn  is  connected  mechanically  with  the  clamp.  As  the  teeth  of  the 
star  wheel  come  in  contact  with  the  control  rod  the  carbon  is  advanced.  The  speed  of  advancing 
depends  entirely  upon  the  position  of  the  control  rod  with  respect  to  the  teeth  of  the  star  wheel — as, 
for  example,  the  shorter  the  distance  between  the  upper  edge  of  the  control  rod  and  the  center  of 
the  star  wheel  the  greater  the  speed  of  feeding  of  the  carbons.  In  the  case  of  the  negative  carbon 
the  position  of  the  control  rod  is  regulated  mechanically  by  a  switch  placed  on  the  outside  of  the 
lamp  housing.  This  control  rod  remains  in  this  fixed  position  until  it  is  changed  mechanically 
by  the  switch  gi\  ing  a  constant  feed  of  the  negative  carl)on  depending  upon  the  siieed  of  rotation 
of  the  negative  carlion  and  the  position  of  the  rod.  If  the  adjustment  of  the  negative  feed  is  incor- 
rect, giving  too  fast  a  feed,  the  point  of  the  carbon  projects  beyond  the  flame,  causing  a  rapid  com- 
bustion of  the  negative  carbon,  so  that  the  distance  between  the  carbons  (the  arc  length)  remains 
practically  the  same.  Inversely,  if  the  feed  is  too  slow  the  rate  of  combustion  slackens  and  tends 
to  keep  the  arc  length  constant.  It  is  only  necessary  to  watch  the  position  of  the  negative  carbon 
on  the  ground-glass  finder  and  make  adjustment  of  feed  about  ever)-  10  minutes.  The  feed  of 
the  positive  carbon,  however,  has  an  additional  electrical  arrangement  governing  the  position  of  the 
control  rod.  On  the  side  of  the  searchlight  drum  is  a  rectangular  box.  This  box  is  so  placed  so 
that  when  the  ray  of  light  from  the  arc  is  reflected  by  means  of  mirroi-s  placed  conveniently  inside 
of  the  drum,  upon  the  first  contact  in  the  bottom  of  the  box  the  metal  contact  becomes  heated  and 
expands,  thereby  closing  an  electric  circuit  which  operates  a  magnet,  which  in  turn  operates  mechan- 
ically the  poedtion  of  the  positive  control  rod.  If  the  positive  carbon  is  in  the  exact  focal  center 
of  the  mirror,  the  ray  of  Light  will  not  fall  on  this  metal  contact  and  the  electric  circuit  will  be  open, 
the  positive  controlling  rod  will  be  down,  and  the  positive  carbon  will  not  be  advancing,  liut  only 
rotating.  There  is  also  a  small  mechanical  device  for  adjusting  the  amount  of  raising  of  the  posi- 
tive controlling  rod  when  the  electric  circuit  is  closed.  The  speed  of  feed  in  this  case  again 
depends  upon  the  speed  of  the  rotating  of  the  positive  carbon  and  the  position  of  the  control  rod. 
Directly  underneath  the  positive  and  negative  section  of  the  carbons  composing  the  arc  there  are 
placed  two  nozzles,  the  larger  nozzle  directlj'  under  the  positive  carbon  and  the  smaller  under 
the  negative.  The  purpose  of  these  nozzles  is  to  give  a  spray  of  vaporized  alcohol  to  the  positive 
aud  negative  carbons,  thereby  preventing  rapid  combustion  of  the  carlions.  The  feeding  of  this 
vaporized  alcohol  is  accomplished  by  having  a  tube  connected  from  the  two  nozzles  to  the  super- 
heater in  the  lamp  housing,  which  in  turn  is  connected  to  the  vaporizer,  which  is  connected  to  an 
electrical  regulating  device  which  regulates  the  supply  of  alcohol  received  from  the  alcohol  tank. 
The  supply  of  alcohol  is  forced  down  to  the  regulator  by  means  of  gravity  pressure. 

The  rheostat  consists  of  a  number  of  resistances  connected  in  a  multiple  arrangement,  part  of 
these  sets  being  connected  across  snap  switches,  thus  enabling  certain  sections  to  be  conveTiiently 
cut  out.  There  are  also  located  in  this  rheostat  two  coil  resistances  which  are  connected  according 
to  the  Wheatstoue  Bridge  principle  with  the  arc  and  another  constant  resistance  in  the  rheostat. 
Those  resistances  are  used  to  operate  the  motor  feeding  the  carbons  together  and  apart  on  the  initial 
lighting  of  the  searchlight.  On  the  outer  side  of  the  rheostat  are  also  placed  terminals  for  the 
ammeter  and  voltmeter  measuring,  respectively,  the  current  consumption  of  the  searchlight  and  the 
line  voltage. 

3.  The  electrical  construction  of  the  searchlight  mechanism  is  as  follows: 
The  essential  electrical  features  are  shown  in  the  diagram.  The  search-light  carbons  are 
connected  through  a  knife  switch  in  series  with  a  resistance  (D)  across  a  constant  direct  supply 
of  120  ^•olts.  The  negative  side  of  switch  (A)  also  is  connected  to  the  negative  carbon  brush 
of  the  striking  motor  used  to  move  the  negative  searchlight  carbon  forward  and  backward 
on  the  ignition  of  the  lamp.  The  positive  side  of  this  motor  is  connected  to  the  positive  terminal 
of  the  switch  (B)  and  through  this  switch  to  mid-point  of  a  resistance  (E),  the  one  terminal  of  whicli 
is  connected  to  the  negative  side  and  the  other  to  the  positive  side  of  the  main  supply.  The  field 
of  the  striking  motor  is  connected  directly  to  the  main  voltage  supply.  The  electrical  arrange- 
ment makes  a  wheatsone  arrangement  in  which  the  arc  and  resistance  D  and  E  (a  and  6)  are  the 
arms  of  the  bridge  and  the  striking  motor  takes  the  place  of  the  galvanometer.     The  annexed 


THE  SEABCHLIGHT. 


89 


diagram  shows  this  arrangement  diagrammatically.  If  the  carbons  are  apart  the  current  in 
the  motor  armature  flows  in  one  direction  due  to  the  state  of  potential  between  the  points 
(X  and  Y)  and  this  direction  of  the  motor  armature  tends  to  luring  the  carbons  mechanically 
together.     As  soon  as  the  carbons  are  together,  the  direction  of   the   current  flowing  through 


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the  motor  will  be  reversed  to  the  state  of  potential  of  points  (X  and  Y).  This  reversed 
direction  of  the  current  tends  to  rotate  the  motor  armature  in  the  opposite  direction,  and 
therefore  the  carbons  are  separated  until  the  potential  difference  between  points  (X  and  Y)  is 
zero;  theu  the  motors  will  be  at  rest.  The  field  excitation  of  this  motor  remains  always  in  one 
direction.  There  is  also  connected 
across  switch  (A)  another  circuit. 
This  circuit  consists  of  a  switch  (F) 
and  a  series-connected  starting  motor. 
Tliis  motor  is  used  for  constant  rotation 
of  the  carbons.  Across  the  positive 
terminal  of  switch  (F)  and  the  nega- 
tive terminal  of  switch  (B)  is  connect- 
ed a  circuit  that  contains  the  solenoid 
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ing rod,  and  in  series  with  this  is  con- 
nected the  contact  switch  (G),  which 
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from  the  arc  strikes  the  metal  con- 
tact of  the  switch.  Also  in  multiple 
with  this  circuit  are  two  multiple 
circuits,  one  containing  a  resistance 
used  in  a  small  tube  to  vaporize 
the  alcohol.  In  the  circuit  is  also  connected  in  series  (not  shown  in  the  diagram)  another  resist- 
ance which  is  used  to  superheat  the  alcohol  vapor.  The  other  circuit  contains  a  magnetic 
solenoid  which  regulates  the  supply  of  alcohol  flowing  through  the  vaporizer.  From  the 
diagram  it  can  be  seen  that  the  circuits  containing  the  arc  and  the  one  containing  the  motor 


120  v:  suppiy 


E=<5r-i-b 


40 


THE   SEARCHLIGHT. 


vised  to  rotate  the  carbons  are  operated  from  tlie  same  switch  (A),  and  the  rcHl  of  tlic  rircuits  can 
oidy  lie  operated  when  both  switches  (A  and  H)  are  closed.  Switch  ((!")  opens  and  closes  the 
circuit  which  contains  a  shunt  motor  used  for  ventilating  fan  (used  to  take  fumes  and  Riisos  from 
searchlight  drum).  A  more  detailed  description  can  be  obtained  from  the  blue  print  under  in- 
dosure  (B). 

4.  The  following  tests  were  coudiicteil: 

(A)  Sun  spot  test  on  mirror. 

(B)  Screen  tests  on  mirror. 

(C)  Concentrated  filament  lamp  test  on  mirror. 

(D)  Heat  run  test  on  searchlight. 

(E)  Voltage  regulation  test  on  projector. 

(F)  Carbon  testa. 

(G^  Night  illumination  tests. 

(H)  Candlepower  measurement  of  s<':ircldia:lit  projeffor. 


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5.  The  German  glass  mirror  manufactured  by  Goet/.  is  44  inches  (110  centimeters)  in  diameter 
and  about  I  inch  thick,  as  against  36  inches  diameter  and  \  inch  thick,  the  pre.-ent  battleship 
standard.  The  focal  length  of  the  German  mirror  is  18i|  inches,  as  against  14J  inches  of  the  Navy 
36-inch  min'or.  The  focal  points  of  the  German  mirror  are  as  strongly  defined  as  the  Baiisch 
&  Lomb  mirror.  The  screen  test  of  the  German  mirror  shows  that  the  surface  is  free  from  irregu- 
larities, and  the  photograph  test  under  indosure  (C^  will  show  that  both  the  German  and  Bausch 
&  Lomb  mirrors  are  about  the  same  in  this  respect.  The  concentrated  filament  lamp  test  showed 
that  the  illumination  of  the  beam  at  a  distance  of  200  feet  of  the  German  mirror  is  slightly  less 
than  that  obt;\ined  from  the  Bausch  &  Lomb  mirror.  The  angle  of  dispersion  of  the  German 
mirror  was  found  to  be  1°  4-5'  as  against  2°  29',  that  of  the  Bausch  k  Lomb  showing  that  the  beam 
of  light  emitted  from  the  German  mirror  is  more  concentrated  than  that  of  the  ISO-inch  Bausch 
k  Lomb  now  in  use.    The  curves  under  inclosure  (D)  are  plotted  with  the  results  obtained. 

The  temperature  rL-e  of  the  outer  casing  of  the  mirror  dome  was  found  to  be  70°  centigiadc. 

The  voltage  regulation  of  the  JSeck  lamp  was  found  to  be  within  10  volts.  This  voltage  vari- 
ation on  the  Beck  arrangement  is  much  greater  than  that  obtained  from  the  General  Electric  Co.'b 
searchlight  now  in  use,  but  the  voltage  regulation  of  the  Beck  lamp  can  be  brought  within  the 
desired  limit  by  a  few  minor  changes.  The  variation  of  \-olfage  does  not  make  as  much  difference 
in  the  Beck  searchlight,  as  the  maintenance  of  the  arc  in  the  focus  of  the  mirror  is  not  de)>endpnt 


THE   SEABOHLIQHT. 


41 


upon  the  voltage  and  thus  a  fluctuation  of  voltage  does  not  change  the  position  of  the  carbons. 
Cur-\-es  plotted  from  the  results  obtained  can  be  found  under  inclosure  (E).  Tests  made  on  the 
carbons  showed  the  following  results: 

The  dimensions  of  the  positive  carbon  are  |  inch  diameter  by  43  inches  length,  as  against  1  [ 
inches  diameter  by  12  inches  in  length,  the  dimensions  of  the  Navy  standard  carbons  now  in 
use,  and  l-^  inches  diameter  by  lOf  inches  length  of  the  Harle  44-inch  searchlight.  The  dimen- 
sions of  the  German  negative  carbon  are  -^  inch  diameter  by  10.7  inches  length,  as  against  1  inch 
diameter  by  7  inches  length,  those  of  the  Navy  standard  36-inch  negative  carbons  now  in  use, 
and  i  inch  diameter  by  10}  inches  length  for  the  Harle  negative.  Both  the  positive  and  negative 
carbons  of  both  types  are  cored.  The  core  in  the  German  positive  carbon  is  made  of  a  composition 
vastly  different  from  those  now  used  and  when  the  German  carbons  burn  in  the  Beck  lamp  there 
is  no  jumping,  flaming,  and  hissing  of  the  carbon  while  burning.  The  German  carbons  burn 
very  evenly  and  the  length  of  burning  of  the  carbons  is  two  and  three-fourths  hours.  With  me- 
chanical changes  in  the  position  of  the  carbon  holders  the  carbons  can  be  burned  for  approximately 
a  period  of  four  hours. 

Comparative  night-illumination  tests  were  conducted  between  the  General  Electric  Co.'s 
Sfi-inch  and  CO-inch  searchlights  and  the  44-inch  Beck  searchlight.     The  German  searchlight 


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beam  was  a  more  concentrated  beam  tlian  that  obtained  from  either  the  30  or  00  inch  beam  of  the 
General  Electric  Co.'s  lamp  and  the  color  of  the  Beck  beam  was  a  whiter  one  than  that  obtained 
from  the  Navy  standard  36  and  60  inch  searchlights.  With  the  carbons  burning  in  a  normal  con- 
dition and  placed  in  the  proper  focal  centers  of  their  respective  mirrors,  foot-randlepower  reading 
at  intervals  of  24  feet  were  taken  across  the  beam  at  a  distance  of  2.850  feet  from  the  searchlight.'^. 
Under  inclosure  (F)  there  will  be  found  four  cross-section  sheets  containing  curves  plotted  from 
the  results  obtained  from  these  night-illumination  tests.  Two  cross-section  sheets  each  contain- 
ing one  curve  showing  the  illumination  across  the  beam  of  the  Beck  searchlight  compared  with 
the  60-inch  General  Electric  searchlight.  These  results  were  obtained  on  August  10,  1914.  From 
these  two  curves  it  can  be  seen  that  the  illumination  obtained  from  the  Beck  Light  is  two  and 
one-half  times  as  great  as  that  obtained  from  the  General  Electric  Co.'s  60-inch  light,  antl  these 
curves  also  show  that  the  illumination  in  the  General  Electric  Co.'s  light  is  more  uniformly  dis- 
tributed acros.s  the  beam  than  that  obtained  in  the  Heck-light  beam.  In  the  Beck  searchlight 
the  beam  shows  a  ver\'  lurge  iHumination  at  the  center  and  falls  off  very  rapidly  at  the  edge  of 
the  beam.  The  other  two  cross-section  sheets  under  inclosure  (F)  contain  the  plotted  result? 


4fi 


THE   SEARCHLIGHT. 


obtained  in  comparing  the  Navy  xtandard  36-inch  pearchlight  with  the  Beck  light.  The  curve 
sheet  containing  the  re.sults  of  the  36-inch  General  Electric  searchlight  consists  of  five  curves. 
The  curves  indicated  by  1,  '1,  and  3  are  plotted  from  actual  results  obtained.  Curve  4  Ls  a  result- 
ant curve  of  curves  1,  2,  and  3  and  curve  No.  5  is  curve  plotted  from  the  theoretical  results  that 
would  have  been  obtained  if  a  41-inch  Navy  standard  searchlight  had  been  used  in  place  of  a 
30-inch  light.  The  other  curve  sheet,  with  the  results  obtained  from  the  Heck  light,  contains 
four  curve.s;  three  plotted  from  the  actual  result.s  obtained,  and  curve  No.  4  is  the  resultant  curve 
of  these  three.  From  the  comparative  data  obtained  it  can  be  seen  that  the  illumination  obtained 
with  the  Beck  searchlight  Ls  about  five  times  as  great  as  that  obtained  from  the  General  Electrii' 
light.     The  spherical  candlepower  of  the  Beck  arc  was  measured  and  the  results  can  be  found 


Fio.  27. 


plotted  under  inclosure  (G).  The  ma.ximum  candlepower  obtained  with  the  use  of  our  present 
Navy  standard  carbons  is  4,500  candlepower,  as  against  84,000  candlepower  obtained  from  the 
Beck  lamp.  This  result  obtained  from  the  Beck  lamp  is  a  trifle  low  in  comparison  with  previous 
results  obtained  abroad,  but  this  is  due  to  atmospheric  conditions. 

6.  In  considering  the  question  of  searchlights  and  their  relative  efliciencies  it  becomes  natural 
to  consider  them  as  made  up  of  the  following  separate  parts: 

(1)  Searchlight  drum,  pedestal,  system  of  control  in  azimuth  and  in  elevation,  shutters. 
•  and  other  purely  mechanical  details. 

(2)  Rheostats. 

(3)  Searchlight  mirror. 

(4)  Lamp  mechanism. 

(5)  Searchlight  arc. 


THE   SEAECHLIGHT. 


43 


One  type  of  searchlight  may  show  increased  efficiency  over  another  because  some  of  these 
parts  have  been  worked  out  to  give  the  very  best  results,  but  a  searchlight  to  give  the  very  best 
results  must  have  all  these  details  wor];ed  out  separately  and  then  joined  together  in  the  proper 
relation  to  give  the  maximum  efficiencies. 

7.  Searchlight  drum  and  other  mechanical  details  are  questions  of  design  which  effect  the 
efficiency  of  the  light  very  little.  They  should  be  worked  out  carefully,  however,  so  that  the 
searchlight  is  properly  lialanced.  may  be  easily  trained  in  azimuth  and  elevation  from  a  distant 
control  station  or  at  the  light  itself.  The  drum  should  be  so  made  that  air  currents  can  not  be  set 
up  inside,  thereby  causing  fliclcerLag  of  the  arc.  ventilation  should  be  sufficient  so  that  light  may 
be  kept  on  at  full  intensity  with  shutter  closed  or  other  means  adopted  for  keeping  the  light  burning 
at  lower  intensities  with  shutter  closed  and  bringing  it  to  full  intensity  instantly  upon  opening  of 
shutter.  It  Is  also  considered  advantageous  to  have  permanent  ammeter  and  volt  meter  mounted 
on  the  seirchlight  drum  or  conne'tioa  on  it  so  that  portable  instruments  can  be  connected.  A 
ground  glass  finder  which  shows  the  position  of  the  arc,  tlie  arc  length,  and  the  variations  of  the 
positive  crater  from  the  focus  of  the  rau-ror  is  considered  an  essential  in  a  properly  designed  search- 


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ight.     The  mirror  should  be  so  secured  that  it  may  be  readily  removed  and  the  miiTor  and  front 
door  strips  should  be  mounted  in  such  a  manner  as  to  eliminate  shock  and  breakage. 

8.  The  searchlight  as  submitted  by  Mr.  Beck  was  not  designed  for  shiplioard  use  but  only  for 
laboratory'  experimental  purposes  and  can  not  justly  l)e  compared  in  regard  to  the  external  mechani- 
cal construction  with  the  Navy  standard  type  now  in  use.  It  has  however  many  mechanical 
featm-es  which  are  considered  advantageous  for  a  searchlight.  Thus  the  method  of  mounting  the 
mirror  and  front-door  strips  are  considered  liefter  than  those  obtained  in  the  past,  the  ground-glass 
finder  of  the  Beck  light  is  of  great  advantage. 

9.  The  rheostat  used  in  connection  ^rith  searchlight  consists  of  two  parts,  a  fixed  and  variaVde 
resistance.  A  certain  amount  of  fixed  resistance  is  necessary'  to  overcome  the  natural  unstalpiUty 
of  a  carbon  arc  and  its  value  must  be,  at  least,  sufficient  to  give  a  voltage  drop  in  the  resistance 
equal  to  one  half  the  arc  stream  voltage.  This  has  lieen  explained  in  more  detail  in  pre^■ious 
report  on  searchlight  carl;on3.  The  variable  resistance  is  neressar.'  in  order  to  obtain  the  pi'oper 
arc  voltage  for  various  carbons  and  various  lengths  of  line.  The  resistance  elements  must  be  of 
sufficient  area  to  carr\'  the  maximum  currents  used  without  undue  heating  of  any  parts  and  of 
such  material  that  the  resistance  does  not  change  excessively  with  temperature  changes.  The 
steps  should  l)e  of  not  greater  than  one  volt  each. 


44 


THE  SEARCHLIGHT. 


The  rheoetat  supplied  with  the  Beck  searchlight  meets  in  general  the  above  requirements. 
It  was  not  constructed  for  shiphoard  use  and  would  refjuire  some  mechanical  changes. 

10.  The  eflSciency  of  searchlight  mirrors  depends  upon  its  truenesa  to  parabolic  form,  its  trueness 
of  svu-face  grinding,  the  color  and  structure  of  the  glass,  and  the  thickness  of  the  glass,  the  losses 
in  searchlight  mirrors  being  due  to  stray  rays  outside  of  the  conical  beam  and  to  absorption  in  the 
mirror.    The  methods  employed  in  the  test  of  mirrors  have  been  described  in  detail  in  past  reports 

by  this  division.  The  intensity  of  illumination  on  a  distant  ob- 
ject, provided  equal  amounts  of  light  to  fall  on  the  mirror,  is  de- 
pendent on  the  efficiency  of  the  mirror  and  the  angle  of  dispersion 
SB  shown  (that  is,  at  a  distance  the  area  of  illuminated  plane).  It 
will  be  noted  that  the  results  on  the  Beck  mirror  test  show  up  poorer 
than  the  Schuckert  or  Bausch  &  Lomb  mirrors  of  36-inch  size. 
Tlie  source  of  illumination  being  the  same  and  the  diameter  of  the 
Beck  mirror  being  greater  and  with  a  smaller  angle  of  dispersion 
we  should  expect  a  greater  foot  candlepower  illumination  with 
this  mirror.  The  results  obtained  show  this  mirror  to  be  less  effi- 
cient than  the  present  ones  in  use  and  with  a  more  efficient  mirror 
still  better  results  would  have  been  obtained  with  the  Beck  light. 
The  relation  between  the  local  lengtli  and  diameter  of  tlie  mirror  should  be  such  that  the 
angle  <t>  (which  is  one-half  the  total  zone  of  light  falling  on  the  mirror)  should  be  such  that  2  in- 
cludes the  majority  of  light  given  off  by  the  arc.  By  increasing  the  focal  length  the  diameter  of 
mirror  remaining  constant  the  ratio  of  the  light  falling  on  the  mirror  to  the  total  given  out  b>-  the  arc 
is  decreased,  but  also  the  angle  of  dispersion  is  decreased  and  therefore  the  correct  focal  length  is  that 
which  changed  in  either  direction  decreases  the  foot  candle  illumination  of  a  distant  object.  If  we 
increase  the  diameter  of  the  mirror  at  the  same  time  as  the  focal  length  is  increased  the  angle  <* 
can  be  maintained  constant  and  at  tl)e  same  time  the  dispersion  decreased,  thus  giving  greater 


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intensity  of  illumination  on  a  distant  object.  On  board  ship,  however,  the  size  of  the  searchlight 
and  thus  the  diameter  of  the  mirror  is  limited  and  service  tests  on  60-inch  searchlights  showed  them 
to  be  unsuited.  However,  it  is  believed  that  the  44-inch  searchlight  (110  centimeters)  is  a  size 
which  can  be  readily  handled  and  that  the  use  of  such  a  size  is  desirable  to  obtain  a  greater  focal 
length  is  also  of  advantage  in  that  it  takes  the  arc  farther  from  the  mirror  and  thus  decreases  the 
chances  of  breakage  of  the  mirror  due  to  the  heat  of  the  arc. 


THE  SEABCHUGHT. 


45 


11.  The  lamp  mechanism  of  a  searchlight  should  be  such  as  to  keep  the  crater  of  the  positive 
carbon  at  the  focus  of  the  mirror,  should  keep  the  arc  length  that  which  is  desired,  should  carry 
the  current  of  the  carbons,  should  contain  mechanism  for  rotating  at  least  the  positive  carbons, 
should  be  sufficiently  rigid  to  keep  the  carbons  in  proper  alignment,  and  should  require  little  care 
and  adjustment. 

12.  The  lamp  mechanism  of  the  Beck  lamp  apparently  meets  all  of  the  above  requirements; 
the  care  required  and  its  ability  to  stay  in  adjustment  will  be  better  determined  by  the  tests  now 
being  carried  out  on  the  Texas.  During  the  tests  conducted  at  this  yard  the  lamp  mechanism 
functioned  very  satisfactorily,  variation  of  the  crater  of  the  positive  carbon  from  the  focus  was 
about  1  millimeter  (hardly  noticeable),  and  the  arc  length  was  kept  practically  constant.  .\"o 
trouble  in  maintaining  the  arc  was  experienced  while  rotating  both  carbons,  the  crater  of  the 
positive  carbon  remained  even  and  there  was  no  noticeable  hissing  and  jumping  of  the  arc.  On 
the  other  hand  while  the  General  Electric  motor  controlled  lamp  mechanism  functioned  success- 
fully maintaining  practically  a  constant  voltage,  the  arc  length  did  not  remain  constant  and  the 
positive  crater  did  not  remain  at  the  focus,  due  to  the  impracticability  of  constructing  positive  and 
negative  carbons  which  will  be  consumed  at  a  certain  ratio.     Also  the  positive  crater  tended  to 


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wander  over  the  surface  of  the  positive  carbon  with  the  result  that  one  side  would  project  and  the 
other  recede,  causing  a  hissing  arc  and  making  it  necessary,  in  order  to  obtain  any  consistent  results, 
to  shut  off  the  light  and  turn  the  positive  carbon  by  hand  about  e-\  ery  1.5  or  20  minutes. 

13.  We  now  come  to  probably  the  most  important  part  of  the  searchlight  and  also  the  one  least 
understood.  There  have  been  numerous  treatises  written  on  the  arc,  probably  the  most  authori- 
tative being  that  of  Mrs.  Ayrton  written  at  least  15  years  ago,  but  it  has  been  always  discussed  from 
the  general  illuminating  side  and  -without  consideration  of  its  uses  for  searchlights.  Paragraphs 
have  been  written  in  some  illuminating  treatises  on  the  searchlight  arc,  but  it  has  in  general  been 
given  scant  attention.  This  is  probably  more  or  less  natural,  for  the  authors  of  these  books  were 
not  especially  interested  in  searchlights  and  as  a  rule  had  had  very  little  experience  with  the 
subject. 

The  desired  searchlight  arc  should  excel  in  the  following  particulars: 

(1)  Small  positive  carbons  with  high  current  densities  per  unit  area  and  thus  high  crater 
temperature  throughout  crater  area,  which  gi\es  high  intrinsic  brilliancy.  Intrinsic  brilliancy 
being  the  number  of  lumens  per  light  source  area. 

(2)  Small  negative  carbons. 


46 


THE  SEABCHUGHT. 


(3)  Loug  arc  length;  that  is,  distance  between  positive  crater  and  negative  point. 

(4)  Uniforiii  mixture  of  rarbon  so  as  to  help  the  evenness  of  burning. 

The  lietk  searchlight  may  be  considered  as  being  especially  designed  to  meet  the  above  re- 
quirements and  therein  lies  its  marked  superiority  over  the  searchliglits  now  in  use.  The  positive 
carbon  is  5  g-inth  diameter  as  compared  to  IJ^-inchee  diameter  of  the  Navy  standard  ;i6-inch  carbons 
and  in  addition  carries  150  amperes  as  compared  to  110  amperes  of  .Vavy  36-ineh.  It  is  of  course 
well  known  that  carbon  is  the  most  refractory  of  all  known  materials,  boiling  at  about  4,000°  *'., 
but  it  unfortunately  commences  to  evaporate  at  a  much  lower  temperature  labout  1,800°  ('.),  so 
that  in  an  ordinary  arc  very  little  of  the  total  area  of  the  end  of  the  positive  carbon  is  at  the  melting 
temperature,  a  small  wandering  spot  being  the  real  elHcient  part  of  the  carbon;  the  rest  of  the  end 
of  the  carbon  is  consumed  at  a  much  lower  temperature,  giving  off  le?s  intense  ravB  and  a  longer 
wave  length.  This  may  be  readily  seen  in  comparison  of  the  Beck  and  ordinary  arc  by  ilie  color 
of  the  arc. 

In  the  Beck  arc  the  ends  of  the  cai'bons  are  enveloped  in  the  hydrocarbon  vapor  which  jjrevents 
the  consumption  of  the  carbons  at  a  lower  temperature  and  allows  the  total  carbon  to  reach  a  much 
higher  temperature,  thus  a  much  greater  current  can  he  utilized  in  a  smaller  iir'-a  itlu-  <  iin-cnt  is 


60 


20' 


20' 


ao' 

oe' 


60'    AVOl£  W  M/VUT£5    ruffAffO 

72'  oisrAMce  /*■  reer 


Fio.  81. 


brought  to  the  carbons  by  roller  contacts  close  to  the  tips).  In  addition  the  positive  carbon  is  cored 
with  a  rare  earth  which  has  a  high  melting  point  (Mr.  Beck  states  that  this  core  melts  at  about 
3,500°  ('.).  When  tlie  arc  burns  the  positive  carbon  develops  a  deep  crater  which  apparently  is 
filled  \vith  an  incandescent  gas. 

The  negative  carbon  of  the  Beck  light  is  -j^-inch  and  is  likewise  enveloped  by  hydrocarbon 
gas  which  allows  a  carbon  of  this  size  to  carry  150  amperes  current.  The  Navy  standard  36-inch 
negative  for  110  amperes  is  1  inch  in  diameter,  although  it  has  been  found  from  tests  on  the  Harle 
light  that  a  heavily  copper-coated  negative  j-^-inch  diameter  would  carry  150  amperes.  The  smaller 
the  negative  the  less  shadow  cast  by  it  and  therefore  the  greater  amount  of  light  flux  falling  on  the 
mirror. 

The  arc  length  of  the  Beck  light  is  maintained  constant  at  about  J^-inch  as  compared  to  about 
^-inch  obtained  at  60  volts  with  the  Xa\y  standard  36-inch  light,  thus  the  longer  length  again 
decreases  the  shadow  caused  by  the  negative.  The  desirability  of  long  arc  length  and  small 
negative  has  been  explained  in  greater  detail  in  pre\-ious  report  on  searchlight  carbons. 

14.  The  luminous  intensity  of  an  object  decreases  with  the  square  of  its  distance  from  the 
searchlight,  but  it  is  not  possible  to  say  that  a  searchlight  which  gives  twice  the  foot-candle  intensity 


THE   SEARCHUGHT. 


47 


at  a  certain  distance  can  be  used  to  pick  up  objects  twice  as  far  as  the  lower  intensity  light.  The 
illuminated  object  acts  as  a  secondary  source  of  illumination,  and  upon  the  intensity  of  illumina- 
tion at  the  observer  from  this  secondary  source  defines  the  ability  to  see  the  object;  this  intensity 
of  illumination  back  from  the  secondary  source  again  decreases  as  the  square  of  the  distance.  There 
should  also  be  taken  into  consideration  the  atmospheric  absorption  which  works  out  to  the  sec- 
ondary source  and  back  again  and  may  be  considered  in  general  as  directly  in  proportion  to  twice 
the  distance. 


Fio.  32. 

For  the  luminous  power  (J,),  which  reaches  the  eye  of  the  observer,  we  have  the  following 
equation: 

J,  =  I4(1=PPK. 

J=Luminous  power  of  the  searchlight. 

L=Distance  of  illuminated  object  (under  the  assumption  that  the  oberver  is  near  the 

searchlight). 
P=Absorption  by  the  atmosphere. 

K=The  coefficient  of  reflection  of  the  illuminated  object. 
Thus  if  we  assume  that  a  searchlight  of  certain  illuminating  capacity  makes  it  possible  to 
easily  distinguish  an  object  at  4,000  meters,  then  a  searchlight  of  four  times  the  illuminating 
capacity  will  carry  5,300  meters,  assuming  that  the  absorption  of  the  atmosphere  is  10  per  cent 
per  kilometer  and  that  the  object  is  equally  well  distinguished  in  each  case. 


48  THE  8EABCHUGHT. 

15.  It  is  very  hard  to  compare  two  scarchlighta  ty  the  eye,  but  during  the  tests  here,  both 
searchlights  were  lighted  (Beck  and  Navy  36-inch)  and  firnt  one  and  then  the  other  were  tumpd 
on  the  same  object  with  the  result  that  objects  not  distinguishabK",  except  in  a  hnzy  way,  with 
the  Navy  36-inch,  were  plainly  outlined  by  the  Beck  light. 

16.  Spectrophotometer  tests  were  planned  but  it  was  found  impossible  to  obtain  a  spectro- 
photometer in  time  for  the  tests.  However,  it  is  apparent  to  the  eye  that  the  Beck  light  is  more 
of  a  bluish-white  light  than  the  standard;  the  ordinary  .HearchliL;ht  biam  looks  yi'Uow  in  com- 
parison. Mr.  Beck  states  that  the  aggregate  quantity  of  blue  and  vicilel  rays  is  about  23  pir  cent. 
At  low  intensities  of  illumination  the  maximum  sensation  to  the  eye  for  the  .xame  .strengths  of 
illumination  shifts  toward  the  blue  end  of  the  spectrum,  while  at  higher  intensities  of  illumina- 
tion the  maximum  sensation  for  same  strengths  is  toward  the  yellow  part  of  the  speilrum.  This 
shifting  of  the  relative  sensations  for  different  intensities  of  illumination  is  a  well-known  phe- 
nomena known  as  the  Purkinje  effect.  It  is  thus  seen  that  the  Beck  light  i."  particularly  good  for 
picking  up  di.-ftant  objects  where  the  illuminative  iiilen?<ily  would  be  small. 

It  is  also  a  well-known  fact  that  a  colored  body  rcdects  the  colors,  from  the  rays  falling  nn  il. 
which  the  body  itself  contains  and  absorbs  the  rays  which  it  does  not  contain,  the  Hick  lighl 
being  strong  in  the  .short  waves  of  light  would  thus  be  particularly  effective  in  picking  up  objects 
of  a  bluish  color,  such  aa  the  various  classes  of  ships  painted  bhiihh  gi-ay. 

17.  It  was  impo.osible,  due  to  the  weather  conditions,  to  make  tests  of  the  Beck  searchlight 
in  foggj'  weather.  Tests  were  made  in  a  light  rain,  but  no  diminution  of  intensity  of  illumination 
at  the  distant  object  could  be  noticed  when  the  illumination  was  measured  with  a  photometer. 


CHAPTEE  4. 
SPERRY  36  AND  24  INCH  HIGH-POWER  SEARCHLIGHT. 


The  Sperry  high-power  searchlight  is  simple  and  automatic,  requiring 
little  attention  while  running  and  few  operations  to  start. 

In  common  with  all  other  types  of  high-power  searchlights,  it  uses 
much  smaller  carbons  and  higher  current  density  (greater  nimaber  of  amperes 
per  unit  area)   than  the  old  pure 


&iernj  Hiak  /nUnstfy  ^n 
KoJhnpgTVG 


Cariov 


Standard  Carion  Jlrc 


carbon  light.      The  negative  car- 
bons are  especially  small. 

The  arcs  of  high-power  lights 
are  ver}-  different  from  those  of 
the  older  searchUghts.  Figure  33 
shows  the  difference  in  appearance 
between  the  Sperry  arc  and  a  low 
power  arc,  both  burning  at  the 
same  amperage.  The  most  appar- 
ent differences  are  in  the  size  of  the 
electrodes  and  in  the  position  of  the 
negative  carbons.  The  slender 
positive  carbon  of  the  Sperry  arc 
allows  the  light  to  be  concentrated 
in  a  much  smaller  crater  than  is 
possible  in  the  ordinary  arc. 

This  concentration  is  a  great 
advantage  in  searchlight  practice, 
since  it  produces  a  searchlight  beam 
having  a  smaller  angle  of  spread; 
that  is,  the  beam  is  more  nearly 
parallel  and  thereforecarries farther. 

The  use  of  a  slender  negative  in 
the  Sperry  arc  causes  the  arc  flame 
issumg  from  its  tip  to  remain  very 
steady  and  prevents  all  wandering 
of  the  negative  "  spot. ' '  Moreover, 
it  gi'eatly  reduces  the  loss  of  light  from  the  crater  by  decreasing  the  size  of 
its  shadow.  The  negative  carbon  is  set  at  an  angle  to  the  positive  carbon 
in  order  that  the  arc  flame  may  sweep  steadily  across  the  mouth  of  the  positive 
crater  and  thus  confine  the  bright  vapors  within  the  crater. 

In  the  crater  itself  lies  the  main  difference  between  the  two  arcs.  Refer- 
ring to  figure  33  it  will  be  noticed  that  the  deep  positive  crater  of  the  SpeiTv 
arc  is  filled  with  an  intensely  bright  vapor. 


Jhaalwe 


Thstiwe 


t^fnfTam* 


Fir;. :«.— Arcs  of  hwh  and  low  power  searchlieht.'i. 


66438—18- 


49 


50  THE   SEARCHLIGHT. 

This  vapor  is  being  constantly  produced  by  the  buniing  of  the  core  of  the 
positive  carbon  and  it  is  produced  in  such  quantities  that  it  bulges  out  against 
the  negative  flame  and  overflows  continuously  at  the  top  of  the  crater.  It  is 
this  overflow  of  bright  gas  above  the  crater  which  causes  the  l)luish  flare  or 
tail  beneath  the  searchlight  beam. 

In  order  to  prevent  the  thin  walled  caater  from  burning  away  at  the  top 
it  is  necessary  to  constantly  rotate  the  positive  carbon.  By  this  means  the 
crater  lip  is  kept  even  and  straight,  making  a  symmetrical  container  for  the 
bright  gas. 

In  the  crater  of  the  pure  carbon  arc  there  is  no  positive  flaTiio  or  bright 
vapor.  The  crater  is  larger  and  shallower  than  the  Sperry  arc  crater,  and  the 
light  comes  entirely  from  the  hot  carbon  surface  of  the  crater  instead  of  from 
any  gas  or  vapor. 

For  the  utilization  of  the  high  intensit}'  arc  to  its  best  advantage  it  has 
been  necessary  to  ilesign  a  mechanism  differing  in  many  respects  from  low  power 
searchlight  apparatus.  The  many  new  and  tlifl'crent  characteristics  of  this 
source  of  hght  demand  lefinements  in  mechanism  and  control  in  order  that  the 
apparatus  may  be  entirely  automatic  anil  may  function  without  the  attention 
of  an  operator. 

The  Sperry  mechanism  has  been  perfected  to  take  care  of  these  new 
functions  entirely  automatically  and  at  the  same  time  it  has  ])cen  kept  simple 
in  operation. 

The  following  is  a  description  of  the  36-inch  searchlight  for  naval  use: 

GENERAL  DESCRIPTION. 

The  control  box  contains  all  the  mechanism  for  rotating  and  feedbig  the 
carbons  and  for  cooling  the  electrode  holdci-s.  A  small  direct-current  motor 
shimted  across  the  arc  supplies  the  motive  power  for  all  the  operations. 

A  small  centrifugal  blower  is  moimted  directly  on  one  end  of  the  motor 
shaft  and  is  operated  normally  at  3,000  revolutions  per  minute.  This  supplies 
a  large  flow  of  air  to  the  hoUow  supporting  columns,  which  couvc}'  it  to  the 
electrode  holders.  The  air  is  then  forced  through  the  electrode  holders  in  such 
a  manner  as  to  abstract  the  surplus  licat  from  the  heads  and  thus  keep  the 
contacts  and  mechanism  of  the  heads  at  a  safe  and  operalile  temperature. 

The  other  end  of  the  motor  shaft  is  fitted  with  a  worm,  which  drives  a  worm 
gear  at  about  90  revolutions  per  minute.  The  worm  gear  is  connected  by  a 
train  of  gears  to  the  shaft  which  extends  from  the  control  box  to  the  ])ositive 
head.  This  shaft,  through  a  beveled  gear  on  the  head,  causes  the  positive 
carbon  to  rotate  at  about  14  revolutions  per  muuitc.  The  rotation  of  the  carbon 
is  necessary  in  order  to  keep  the  thin-walled  crater  bm-ning  sjanmetrically. 

Besides  rotating  the  positive  carbon  and  air  cooling  the  heads,  the  motor 
also  supplies  the  driving  power  for  feetlmg  the  negative  carbon.  The  negative 
carbon  is  the  sensitive  electrode  of  the  arc.  A\l  variations  ui  arc  voltage  are 
compensated  for  by  the  motion  of  the  negative  carbon  either  forward  or  back- 
ward. 

In  striking  the  arc  it  is  the  negative  which  runs  up  to  the  positive,  makes 
contact,  and  then  di-aws  back  to  the  proper  arc  length. 


FIG.  34.-SPERRY  36-INCH  HIGH  POWER  SEARCH- 
LIGHT. FRONT  AND  RIGHT  SIDE.  IRIS  SHUTTER 
PARTLY    CLOSED. 


FIG.  35.-SPERRY  36-INCH   HIGH   POWER  SEARCHLIGHT   LAMP.       THREE-QUARTER  LEFT  SIDE 

VIEW. 


THE   SEAECHLIGHT.  51 

Tliis  arrangement  allows  the  positive  carbon  to  be  entirely  independent 
of  all  varying  conditions  and  allows  the  positive  crater  to  be  held  ia  a  fixed 
position  by  means  of  a  thermostatic  control,  desci'ibed  later. 

The  negative  carbon  is  regulated  by  the  voltage  across  the  arc,  and  tends 
to  inaintaui  a  constant  voltage  by  feeduig  either  forward  or  baclnvard.  During 
normal  operation  the  arc  has  a  voltage  of  75  volts  and  an  arc  length  of  1  inch; 
the  negative,  by  keeping  the  voltage  constant,  therefore,  keeps  the  arc  length 
practically  constant  as  weU. 

The  mechanism  for  accomplishing  this  control  is  mounted  as  a  complete 
unit  in  the  control  box.  It  comprises  a  small  horizontal  lever  arm  pivoted  in 
the  middle.  To  one  end  is  fastened  an  adjustable  spring  and  from  the  other  is 
suspended  the  plunger  of  a  solenoid,  which  is  connected  across  the  arc.  On 
this  balanced  arm  are  mounted  two  pairs  of  pawls  so  pivoted  that  either  one 
pair  or  the  other  can  engage  with  one  or  the  other  of  two  opposed  ratchet 
wheels  which  are  mounted  on  the  same  shaft.  This  shaft  is  connected  by 
beveled  gears  to  the  negative  feed  shaft.  This  system  of  pawls  is  caused  to 
reciprocate  constantly  by  means  of  a  rod  and  eccentric  driven  by  the  control- 
box  motor.  Normally  none  of  the  pawls  touch  the  ratchets,  since  75  volts 
across  the  solenoid  just  balances  the  puU  of  the  spring.  But  when  the  arc 
voltage  changes  the  balance  is  upset,  the  beam  tips  either  one  way  or  the  other, 
and  causes  one  of  the  two  pairs  of  pawls  to  engage  with  the  ratchet.  The 
reciprocation  of  the  pawls  then  causes  the  ratchet  to  turn,  and  this  rotates 
the  feed  shaft,  feeding  the  negative  either  forward  or  backward  as  the  case 
demands  untU  75  volts  is  reestablished,  whereupon  the  pawls  agaui  disengage 
from  the  ratchets.  This  same  mechanism  is  used  for  striking  the  arc.  It 
operates  as  follows: 

When  the  maia  switch  is  thro\\Ti  in,  line  voltage  is  applied  to  the  motor 
and  the  voltage-control  solenoid.  The  motor  immediately  speeds  up  to  over 
5,000  revolutions  per  mmute  and  causes  rapid  reciprocation  of  the  pawls.  The 
excessive  voltage  on  the  solenoid  pulls  down  the  plunger,  which  causes  the  pawls 
to  rapidly  turn  the  ratchet  and  feed  the  negative  toward  the  positive.  When 
the  negative  touches  the  positive  the  voltage  drops  down  to  about  30  volts; 
this  decreases  the  solenoid  puU,  changing  the  balance  of  the  lever  and  causing 
the  other  pair  of  pawls  to  engage  in  the  ratchet;  the  negative  is  then  drawn 
back,  lengthening  the  arc  until  an  arc  voltage  of  75  volts  is  obtained,  whereupon 
the  pawls  disengage. 

This  system  of  arc  control  is  so  balanced  that  it  will  work  in  all  positions 
from  horizontal  to  vertical  without  any  readjustments. 

The  positive  head  or  electrode  holder  consists  of  a  bronze  casting,  through 
which  the  positive  carbon  is  fed.  The  front  portion  of  this  casting  consists  of 
heat-radiating  vanes,  through  which  the  air  is  forced.  A  small  fiuartz  bushing 
is  mounted  in  front  of  the  radiating  vanes  and  is  held  in  place  by  a  brass  cap, 
which  also  covers  the  heat-radiating  vanes.  The  quartz  bushing  acts  as  a  pro- 
tecting collar  to  that  part  of  the  positive  carbon  which  protrudes  from  the 
holder. 

This  bushing  serves  two  purposes,  first,  being  a  heat  insidator,  it  keeps 
the  carbon  extremely  hot  near  the  crater,  where  excessive  temperature  causes 


52  THE   SEARCHLIGHT. 

an  increase  in  light.  Secondly,  it  prevents  excessive  tapering  of  the  positive 
carbon  by  shielding  the  liottost  part  from  air  currents. 

The  rotating  nieinbor  of  the  positive  head  clamps  the  carbon  by  means 
of  two  small  knurled  steel  wheels,  which  carry  the  carbon  with  them,  thus 
rotating  it  without  feeding  it  forward. 

The  positive  feed  is  ol;tained  by  means  of  a  star  wlicel,  attached  through 
a  worm  gear  to  one  of  the  two  feed  wheels,  and  a  rod  which  can  be  raised  into 
enHajiement  with  this  star  wheel. 

Normally  the  rod  is  out  of  engagement  with  the  star  wheel,  and  tlie  posi- 
tive carbon  is  rotating  without  feeding.  Wlien  it  is  necessarj'  to  feed  the  car- 
bon forward,  the  rod  is  raised  either  by  the  thermostat  control  or  by  hand. 
The  star  wheel  then  hits  the  rod  once  each  turn  of  the  rotating  member  and  is 
itself  turned  a  point.  This  rotates  the  feed  wheels  on  the  carbon  and  causes 
the  carbon  to  move  forward  about  one-fiftieth  of  an  inch  each  rotation. 

The  control  box  contains  two  small  magnets,  which  are  actuated  by  the 
thermostat.  When  the  thermostat  contacts  close,  the  magnets  operate  to  lift 
the  pointed  feed  rod  into  engagement  with  the  star  wheel.  This  is  more  fiUly 
described  under  a  separate  heading. 

The  negative  electrode  holder  is  smaller  tlian  the  positive.  It  is  possible 
to  make  the  negative  holder  very  small  and  comjiact,  since  the  negative  car- 
bon is  not  rotated  and  since  there  is  only  one-sixth  as  much  heat  generated  at 
this  electrode  as  is  generated  at  the  positive  electrode.  This  eliminates  the  rotat- 
ing devices  and  the  elaborate  cooling  means,  so  that  the  negative  holder  consists 
only  of  the  contacts  and  tlie  feed  rollers. 

A  small  amount  of  air  passes  through  the  negative  head  for  cooling  pur- 
poses, but  this  is  less  than  10  per  cent  of  the  flow  through  the  positive  head. 

The  head  consists  of  a  split  casting.  The  lower  half  is  attached  to  the 
supporting  column,  the  upper  half  is  hinged  and  pressed  against  the  lower  half 
by  a  spring  and  lever. 

The  carbon  is  forced  through  between  the  contacts  separating  the  two 
jaws  slightly,  thus  insuring  good  contact  between  holder  and  carbon.  The 
carbon  is  gripped  and  fed  V)y  two  knurled  hard  steel  feed  wheels  at  the  rear  of 
the  head.  These  are  pressed  against  the  carbon  by  means  of  a  steel  spring 
connecting  their  supporting  arms. 

The  wheels  are  geared  to  the  feed  shaft,  which  extends  from  the  head 
down  into  the  control  box,  where  it  is  connected  by  a  beveled  gear  to  the  voltage 
control  mechanism. 

In  recarboning  tlie  negative  the  head  is  turned  sideways  through  a  small 
angle  so  that  the  carbon  may  be  inserted  without  hitting  the  positive  head. 
The  turning  of  the  negative  head  also  spreads  the  feed  rollers  apart,  thus  releas- 
ing the  grip  on  the  carbon  and  facilitating  recarboning.  With  this  arrange- 
ment for  recarboning,  it  is  possible  to  reduce  tlie  time  that  the  light  is  out  for 
retrimming  to  less  than  one  minute.  This  feature  is  of  great  importance  in 
sen^ice,  since  the  renewal  periods  are  reduced  to  a  point  where  the  light  may 
be  considered  as  of  practically  continuous  value. 

The  lamp  mechanism  unit,  complete,  weighs  only  80  pounds.  Two 
handles,  one  at  each  end  of  the  control  box,  make  the  lamp  easily  portable. 
Tlie  lamp  is  held  in  the  drum  by  two  guides  in  which  it  sUdes.     It  may  be 


FIG.    36.-SPERRY    36-INCH    HIGH    POWER    SEARCHLIGHT    LAMP.      THREE-QUARTER    RIGHT    SIDE 

VIEW. 


FIG.    37.— SPERRY    36-INCH    HIGH    POWER    SEARCHLIGHT.       RIGHT    SIDE    VIEW.      0°  ELEVATION. 


THE   SEAKCHLIGHT.  53 

moved  forward  or  back^va^d  in  the  guides  for  spreading  the  beam  by  means 
of  a  focusing  screw  which  extends  from  the  back  of  the  control  box  out  through 
the  rear  casting  of  the  drum  lamp  compartment. 

The  drum. — The  drum  is  constructed  of  1/16-inch  sheet  brass,  supported 
front  and  rear  by  two  ring  castings.  The  front  ring  casting  holds  the  shutters 
and  the  front  door;  the  rear  casting  supports  the  mirror  and  frame. 

At  the  top  of  the  drum  is  a  ventilating  hood  which  contains  a  motor  and 
blower  for  the  forced  ventilation  sj^stem.  A  forced  ventilation  system  is 
necessary  in  the  operation  of  a  high-intensity  searchlight  for  two  reasons: 

(1)  The  heat  of  the  arc  is  much  greater  than  the  heat  from  the  old-style 
carbon  arc.     This  necessitates  cooling  the  mirror  and  the  drum. 

(2)  The  high-intensity  arc  gives  off  a  certain  amount  of  white  fumes, 
wliich  must  be  carried  off  to  prevent  their  deposition  on  the  front  door  and 
mirror. 

The  ventilation  system,  in  its  present  form,  performs  all  of  these  functions 
very  efSciently.  The  air  is  first  taken  in  under  the  weather  protecting  hood 
at  the  top  of  the  mirror  dome;  it  is  then  drawn  down  over  the  back  of  the 
mirror  through  the  cooling  space  betvreen  the  spun  metal  mirror  protecting 
dome  and  the  mirror  itself.  At  the  bottom  of  the  mirror  the  air  passes  through 
two  ducts  which  carry  it  into  the  drum. 

The  air,  however,  can  not  be  allowed  to  escape  directly  into  the  lower 
part  of  tiie  drum,  as  the  currents  would  cause  severe  flickering  of  the  arc.  It 
is,  therefore,  gmded  by  means  of  two  flat  ducts  up  around  either  drum  side. 
This  has  the  desired  cooling  effect  on  the  drum  and  mirror  frame  and  at  the 
same  time  eliminates  all  drafts  around  the  arc. 

The  ah-  is  hberated  from  the  guiding  ducts  very  near  the  top  of  the  drum, 
and  is  from  this  point  forcibly  sucked  to  the  exhausting  fan  which  is  at  tlie 
top  of  the  drum  just  over  the  arc.  The  air  then  passes  out  tlirough  a  liglit- 
baffling  hood.  The  temperature  of  this  exhaust  air  normally  runs  about  60° 
above  the  outside  temperature.  The  mirror  is  effectively  cooled  by  this  scheme, 
and  no  breakage  has  yet  been  recorded. 

Another  important  factor  in  the  ventilation  system  is  the  utilization  of 
the  cooling  blast  of  air  which  passes  through  the  positive  holder  for  caiTying 
off  the  arc  fumes.  On  the  brass  cap  which  fits  over  the  coohng  chamber  of  the 
positive  head  are  placed  two  small  brass  vanes  just  over  the  air-outlet  port. 
These  vanes  are  so  turned  as  to  direct  the  air  blast  exactly  toward  the  exhaust 
fan.  The  arc  flame,  it  is  found,  exhausts  itself  du'ectly  hito  this  blast  of  air, 
and  all  the  arc  fumes  are  thus  entrained  by  this  blast.  Therefore,  by  guiding 
the  blast  to  the  exhaust  fan  the  fumes  also  are  completely  carried  off  and  do 
not  eddy  and  swirl  in  the  drum.  This  pomt  is  of  extreme  importance  m  ver- 
tical operation'of  the  light,  since  the  air  blast  is  strong  enough  to  carry  the 
fumes  horizontally  from  the  arc  to  the  exhaust,  thus  preventmg  excessive 
fuming  of  the  front-door  strips  at  the  higher  angles  of  elevation. 

It  is  always  advisable  when  replacing  the  brass  cap  to  observe  carefully 
the  direction  of  the  vanes  and  ak  currents  from  the  new  cap.  Any  disarrange- 
ment is  made  evident  b}-  excessive  cloudmg  of  the  door  or  mirror. 

Oil  the  right-hand  side  of  the  drum  above  the  bare  which  support  the 
trunnion  is  mounted  a  weatherproof  box  with  a  door  and  padlock.     This  box 


54  THE   SEARCHLIGHT, 

contains  all  the  instruments  for  regulating  and  observing  the  arc.  Tho>o  are 
the  thermostat,  the  gi-ound-glass  finder,  the  arc  length  regulator,  and  a  peep- 
sight.  The  box  is  accessible  to  the  operator  in  all  positions  of  the  searchlight 
from  horizontal  to  vertical. 

'llie  ground-glass  fintler  is  a  simple  and  compact  lens  system  which  gives 
a  full-size  image  of  the  arc,  right  side  up,  on  a  small  square  of  ground  glass. 

The  proper  positions  of  the  two  electrodes  are  marked  on  the  ground  glass, 
so  that  the  operator  can  at  all  times  determine  whether  tlio  crater  is  in  focus 
without  watching  the  beam  itself.  lie  may,  fuithermore,  watch  the  behavior 
of  the  arc  image  from  which  he  can  legulate  negative  and  positive  feetl  and 
amperage. 

The  negative  regulator,  or  arc  length  regulator,  is  placed  just  below  the 
finder.  It  consists  of  a  small  adjustable  resistance  connected  in  series  with 
the  solenoid  of  the  voltage-control  mechanism.  Increasing  the  resistance  with 
the  series  rheostat  weakens  the  solenoid  jjull  and  thus  causes  the  arc  length 
to  increase  until  the  arc  voltage  increases  sufTiciently  to  re-establish  the  equi- 
librium of  the  pawl  system.  Decreasing  the  resistance  causes  a  similar  reduc- 
tion in  arc  voltage,  and,  consequently,  in  arc  length. 

The  positive  feed  is  controlled  by  means  of  a  theiinostat  which  is  located 
in  the  instrument  box.  The  operator,  however,  does  not  have  to  relj*  on  the 
automatic  thermostat  control,  and  in  emergencies  may  use  a  push  button 
which  is  mounted  on  the  thermostat  case,  thus  feeding  the  positive  by  hand. 

THERMOSTAT    COXTROl.    OF    POSITIVE    ELECTRODE. 

The  function  of  the  thermostat  is  to  maintain  the  positive  crater  of  the 
arc  at  the  focus  of  the  parabolic  muror.  While  the  arc  is  burning,  the  positive 
carbon  is  being  rapidly  consumed.  This  must  be  compensated  for  by  feeding 
the  carbon  forward  sufficiently  to  hold  the  crater  in  a  fixed  position.  The 
thermostat  accomplishes  this  by  closing  an  electrical  circuit  when  the  crater 
has  burned  back  out  of  focus.  This  ch-cuit  energizes  the  thermostat  magnets 
located  in  the  control  box  of  the  searchlight  lamp,  which  then  causes  the  i)osi- 
tive  electrode  to  feed  forward  as  described  under  the  positive  feeding  mechanism. 

The  positive  crater  of  the  arc  is  in  the  center  Ime  of  the  drum.  On  the 
side  of  the  drum  opposite  the  mstrument  box  is  a  small  concave  miiTor  of  such 
a  focal  length  as  to  concentrate  the  rays  from  the  arc  into  a  sharp  nanow 
beam  on  the  instrument  side  of  the  drum.  Exactly  opposite  to  this  mirror  is 
a  narrow  slit  m  the  drum,  behind  which  is  located  the  sensitive  clement  of  the 
theraiostat.  The  line  joining  the  center  of  the  mirror  and  the  thermostat 
element  is  slighth*  in  front  of  the  crater  so  that  direct  light  from  tlic  crater 
will  not  fall  on  the  thermostat  strip.  The  function  of  the  mirror  is  to  focus 
the  hght  from  the  positive  crater  in  a  narrow  strip.  The  radius  of  curvature 
of  the  niiiTor  is  such  that  the  focus  will  be  at  the  same  distance  from  the  minor 
as  the  thermostat  element  is.     The  operation  is  as  follows: 

Wlien  the  positive  crater  is  at  the  focus  of  the  parabolic  mirror,  the  position 
of  the  thermostat  mirror  is  adjusted  so  that  the  strip  of  light  falls  on  the  theiTiio- 
stat  element.  As  the  crater  burns  back,  the  stri|)  of  reflected  light  naturally 
moves.  As  the  thermostat  is  more  than  twice  as  far  from  the  mirror  as  the 
positive  crater,  the  strip  of  light  moves  more  than  twice  as  fast  as  the  posi- 


THE   SEARCHLIGHT.  55 

tive  burns  away.  This  adds  materially  to  the  sensitiveness  of  the  arrangement. 
As  soon  as  the  strip  of  light  has  moved  off  the  sensitive  element,  the  thermostat 
closes  the  controlling  circuit  which  feeds  the  positive  up  until  the  light  strip 
is  agaia  on  the  element.  Then  the  circuit  is  reopened  until  the  crater  has  again 
burned  back. 

The  coastruction  of  the  thermostat  is  extremely  simple.  It  consists  essen- 
tially of  two  zinc  strips  as  sensitive  elements.  One  strip  is  -exposed  so  that  it 
will  be  struck  by  the  beam  of  light,  while  the  other  is  protected  from  it.  These 
strips  are  fixed  at  one  end.  The  other  end  of  each  strip  is  attached  to  the 
short  arm  of  a  lever.  At  the  extremity  of  the  long  lever  arms  are  fixed  platinum 
contacts.  The  zinc  strips  are  held  in  tension  by  means  of  springs.  Now 
when  the  light  beam  falls  on  the  exposed  zinc,  the  zinc  is  heated.  It  expands 
and  the  contactor  arm  is  pulled  back  by  the  spring.  The  contacts  are  then 
separated.  As  the  spot  of  light  moves  off  the  zinc,  the  zinc  cools,  contracts, 
and  pulls  the  contactor  arm  over  until  the  contacts  meet  and  the  circuit  is 
closed.  The  motion  of  the  zinc  strip  is  considerably  amplified  by  the  l6ver 
an-angement,  so  that  the  thermostat  is  not  only  very  sensitive,  but  the  circuit 
is  made  and  broken  with  comparative  rapidity — a  point  to  be  desired.  The 
object  of  the  second  zinc  strip  is  to  compensate  for  all  temperature  changes  in 
the  instrument  box  itself.  If  the  temperature  in  the  instrument  box  changes, 
both  strips  expand  or  contract  equally,  so  that  the  action  of  the  thermostat 
is  not  affected. 

The  multiplying  arms  of  the  thermostat  are  counterbalanced  by  small 
adjustable  weights  at  the  top  so  that  the  instrument  is  not  subject  to  vibration 
or  jars.  The  tension  in  the  exposed  zinc  strip  is  adjustable  to  the  desired 
sensitiveness  by  means  of  a  thumb  lever  screw  projecting  through  the  bottom 
of  the  case.  The  thermostat  can  be  taken  out  of  its  case  without  any  trouble, 
as.it  is  not  necessary  to  open  any  electrical  connections.  To  take  it  out,  it  is 
merely  necessary  to  remove  the  sliding  cover  and  loosen  the  set  screw  on  the 
instrument.  The  current  is  brought  to  the  thermostat  by  means  of  copper 
strips  and  springs  which  make  contact  when  the  instrument  is  in  place.  Thus 
the  thermostat,  which  is  by  far  the  mogt  sensitive  part  of  the  entire  searchlight, 
is  readily  removed  for  inspection.  The  tension  on  the  zinc  strip  can  be  ad- 
justed from  the  outside,  as  can  the  position  of  the  thermostat  mirror,  so  that 
the  position  of  the  positive  crater  can  be  regulated  without  opening  anything. 
The  thermostat  contacts  can  be  viewed  through  a  small  window  containing  a 
lens,  so  that  their  size  is  magnified.  In  this  way  the  attendant  can  assure 
himself  of  the  proper  operation  of  the  instrument. 

The  contacts  of  the  thermostat  are  shimted  by  means  of  a  condenser  and 
resistance,  so  that  arcing  is  reduced  to  a  minimum.  Hence  there  is  little  ten- 
dency towards  pyramiding  or  burning  the  contacts,  and  the  sensitivity  of  the 
thermostat  is  not  impaired.  On  the  thermostat  case  is  mounted  a  small  push 
button,  by  means  of  which  the  control  circuit  may  be  closed  independently 
of  the  thermostat,  so  that  the  positive  may  be  fed  by  the  attendant,  if  desired. 
However,  after  the  thermostat  is  adjusted  the  lamp  will  operate  automatically.. 

An  ammeter  is  also  mounted  on  the  drum  in  a  weatherproof  box.  This  is 
so  situated  that  the  operator,  standing  at  the  instrument  box,  may  easily  read 


56  THE   SEARCHLIGHT. 

the  ammeter  scale.  A  waterproof  switch  is  mounted  near  the  instrument  hex 
which  controls  the  exhaust  blower  motor  at  the  top  of  the  drum. 

Two  shutters  arc  furnished  with  each  searchlight,  an  iris  shutter  and  a 
Venetian-blind  shutter.  The  iris  shutter,  which  is  entirely  light-tight,  is 
operated  by  means  of  a  small  handwheel  at  the  side  of  the  drum.  The  Venetian 
blind,  or  signaling  shutter,  is  operated  by  a  handle  just  above  the  iris  shutter 
handwheel. 

The  main  switch  is  located  in  the  front  part  of  the  lamp  compartment,  and 
is  operated  by  a  handle  on  the  outside  of  the  lamp  compartment. 

All  of  these  controls  are  on  the  same  side  of  the  drum,  so  that  the  operator 
at  no  time  has  to  leave  his  post  to  p(nform  any  operation  about  the  light. 

Two  large  doors,  one  on  either  side  of  the  drum,  afford  easj'  access  to  tiio 
interior  for  recarboning  or  cleaning  the  mirror. 

BEAM    COLOR. 

The  color  of  the  beam  of  the  Sperry  high-power  searchlight  is  an  intense  blue- 
white,  whereas  the  beam  of  the  low-power  searchlight  appears  a  dim  yellow  by 
comparison.  This  blue  color  is  a  very  important  advantage  of  the  Sperry 
searchlight  and  has  a  great  military  value.  As  is  well  known,  it  is  the  universal 
practice  of  all  navies  to  paint  battleships  and  all  other  naval  vessels  a  bluish- 
grav  color  called  battleship  gray.  The  reason  for  the  adoption  of  this  paint  is 
to  make  the  object  as  inconspicuous  as  possible  by  causing  it  to  blend  with  the 
background.  In  the  case  of  ships  at  sea  where  the  background  is  blue  sky, 
blue  water,  or  gray  mist,  the  most  effective  paint  color  for  blending  with 
this  is  bluish-gray  and  has  been  adopted  generally  as  war  paint.  At  night 
searchlights  can  pick  this  color  out  with  more  or  less  success,  depending  on  the 
color  of  the  beam.  It  is  in  this  respect  that  the  Sperry  light  is  superior  to  low- 
power  lights,  for  its  beam  contains  largely«.just  the  hght  which  the  blue-gray 
reflects.  A  gray  ship  illuminated  with  the  high-power  light  glistens  with  a  bluish 
hue,  but  with  the  ordinary  yellow-beam  searchlights  the  gray  target  only  reflects 
a  dull  colorless  light. 

-Vnother  advantage  in  the  blue  color  is  the  well-known  fact  that  with  very 
low  intensities,  such  as  obtain  at  the  ultimate  ranges  of  the  searchlight,  blue  is 
the  most  visible  color  and  can  be  seen  at  greater  distances  than  the  same 
intensity  of  red  or  yellow. 


THE   SEAKCHLIGHT, 


Fig.  3S.— Sperry  3R-incli  hinh-power  searchlitiit.    Names  of  parts. 


1= 

2 

3^ 

4^ 

5= 

6. 

1- 

,S= 

9= 
10. 
11. 
12 
13 
14= 
15. 
16- 
17- 


Ventilator  hood — housing  for  ventilator  motor. 

Instrument  box. 

Groimcl  glass  Qnder. 

Thermostat  pu.sh  button— hand  feed  of  positive. 

Thermostat— automatic  positive  feed. 

Arc  length  regulator. 

Protecting  hood  over  air  inlet. 

.Vir  inlet  for  coo'in?  and  ventilating. 

Mirror  dome  for  protection  of  mirror. 

Elevation  scale  and  pointer. 

Elevation  rack. 

Elevation  handwheel. 

Elevation-handwhee!  locking  clarap. 

Focussing  screw  handle  for  moving  lanip  in  drum. 

Sliding  door  for  access  to  lamp  mechanism. 

Bottom  door  in  lamp  compartment  for  removing  dirt. 

Snap  switch  for  ventilating  motor. 


IS=  Baffled  slot  for  air  outlet  from  exhaust  fan. 

19=  Removable  Venetian  blind  shutter  unit. 

20"=  Handle  for  Venetian  blind  shutter  unit. 

21=  Handle  for  jront-door  unit. 

22=  Small  lamp  container  for  illuminatin,g  ammeter  and 

elevation  scales. 
23=  -Vmmeter  seen  through  gla.ss  protecting  ttindo\\;. 
24=  Snap  switch  for  dial-illuminatmg  lamp. 
25=  Positive  carbon  tube — for  protection  of  exposed  end. 
26=  Handle  tor  operation  of  Venetian  bimd  shutter. 
27=  Handwheel  for  operation  of  iris  shutter. 
2S=  Sliding  door  and  handle  for  access  to  drum. 
29=  Clamp  for  holding  shutter  unit. 
30=  Main  switch  handle. 

31=  Snap  smtch  for  lamp-illuminating  azimuth  scale. 
32=  Handhole  cover  in  base. 


58  THE   SEARCHLIGHT. 


1»  Upper  contact  shoe— negative  head. 
2-Smallcup  forciitclilng  particles  from  the  negative  carbon. 
3—  Lever  for  pressing  upper  contact  shoe  against  the  carbon. 
4— I^ever  spring. 

5—  Spring  for  holding  feed  rollers  against  the  carbon. 

6—  Steel  food  rollers . 

7=»  Carbon  releasing  toggle  for  spreading  apart  the  feed  rollers. 

8>"  'joars  connecting  food  shaft  to  food  rollers. 

9—  Lower  contact  shoe  rigidly  mounted  on  supporting  column. 
10=-  Negative  feed  rod  extending  from  negative  head  to  voltage  control  mechanism. 
1 1= Supporting  strip  for  negative  column. 
12- Carbon  releasing  shaft. 

1.3=  Negative  supporting  column  of  hollow  tubing  for  carrying  air  to  the  head. 
11—  Tray  for  catching  particles  dropped  from  the  arc. 
15=«  Spring  and  plunger  to  prevent  turning  of  the  nogatlvo  head. 
16=  Counterbalance  on  the  arm  of  the  voltage  control  mechanism. 

17—  Rear  guide  for  supporting  lamp  in  drum. 

18—  Handle  for  hand  operation  of  positive  feeding  mechanism. 

19—  Voltage  control  spring  balancing  solenoid  pull. 

20—  Crank  for  hand  feed  of  the  negative  electrode. 

21—  Upper  pawl— voltage  control  mechanism. 

22—  Clamp  for  holding  brass  side  plate  on  the  lamp  mechanism  box. 
23— Lower  pawl— voltage  control  mechanism. 

21— Tvvo  opposed  ratchet  wheels  into  which  the  pawls  mesh. 

25=  Reciprocating  member  carrying  the  four  pawls. 

26—  Voltage  control  solenoid. 

27=  Reciprocating  rod  and  joint— voltage  control  mechanism. 

23—  Centrifugal  blower  for  air  cooling  of  the  electrode  holders. 
29=  Motor  for  driving  feeding  mechanism  and  blower  fan. 
30=  Thermostat  magnets. 

31=  Thermostat  magnet  armature  forllftlngfoed  rod. 

32=  Eccentric  for  reciprocation  of  tho  voltage  control  mechanism. 

33—  Worm  gear  case,  reducing  motor  speed  for  rotation  of  positive  carbon. 

34—  Main  leads  carrying  current  to  the  arc. 

35— Connection  from  thermostat  magnets  to  thermostat. 

36—  Voltage  regulator  connection  from  solenoid  to  variable  resistance  in  tho  Instrument  box. 

37=  Front  guide  for  supporting  lamp  iu  drum. 

38—  Gear  train  from  worm  gear  shaft  to  positive  rotating  shaft. 

39=  Handle  for  carrying  lamp. 

40=  Block  insulating  positive  head  from  the  control  box. 

41-Casting  for  holding  tho  supporting  stays. 

42=  Nut  for  tightening  supporting  stays  and  aligning  tho  heads. 

43=  Mica  insulation  on  positive  column. 

44=  Positive  column  supporting  stays. 

43=  Positive  column  of  hollow  tubing  for  carrying  air  to  the  positive  head. 

46-  Positive  feed  rod. 

47— Main  loads  from  positive  column  to  silver  contacts. 

48—  Rod  for  rotating  positive  carbon. 

49— Spring  for  retaining  food  rod  in  tho  "out"  position. 

50— Gear  on  rotating  rod  meshing  with  rotating  member  of  positive  head. 

51— Point  on  feed  rod  raised  to  hit  star  wheel. 

52—  Roller  bearing  for  rotating  member  of  positive  head. 

53-CircuIar  gear  on  rotating  member  of  head. 

54—  Food  wheels  (star  wheel  not  visible  in  cut). 

55—  Spring  holding  brass  cap  and  quartz  bushing  in  place. 

56—  Brass  cap  and  vanes  fitting  over  cooling  chamber. 

57—  Quartz  bushing. 


3         2  / 


Zl       2^      25       ?6      27      28     29       50      21      52       52.      54- 

FIG.    39.— SPERRY    36-INCH     HIGH     POWER    SEARCHLIGHT     LAMP.       NAMES    OF     PARTS. 


THE  SEABCHLIGHT. 


59 


The  performance  of  the  Sperry  high-power  searchhght  may  best  be  shown 
by  the  report  of  the  test  made  on  sample  lamp  supphed  to  the  Navy  Yard, 
New  York.  A  copy  of  this  report  is  given  below.  The  searchlight  used  con- 
sisted of  a  low-power  36-inch  drum  modified  to  accommodate  a  Sperry  high- 
power  lamp.     A  searchlight  of  this  type  is  known  as  a  converted  searchlight. 

Report  of  Test  ok  U.  S.  S.  Maine — ^Modified  Low-Power  36-inch  Se.vrchlight  to  High 
Power  by  the  Sperry  Gyroscope  Co. 

[JUNE  1,  1917] 

Tests  have  been  conducted  by  this  dudsion  on  a  Na\'y  standard  36-inch  low-power  searchlight, 
which  was  converted  by  the  crew  of  the  Mame  to  a  36-inch  high-power  searchlight,  the  necessary 
parts  being  supplied  by  the  Spern,'  Gyroscope  Co.    These  tests  were  conducted  to  determine  the 


Thermostat 


KJE.C3.FsLt.oRHC-> 


E.LtV.  5CAUt  \J^M» 


dM*.t>  ^vriT&H 


Fir,.  40. 


AvZ.\M\JTV-l  5cA.v.tUhMP 


;>!.»*».»  ;9WtT^H 

-Sperr.v  3fi-inoh  'ni;h-nower  searchlight  'hand  control). 


Wiring  diagram. 


desirability  of  placing  orders  for  parts  to  cover  the  conversion  of  a  large  number  of  these  old  lamps 
and  to  determine  the  characteristics,  operation,  and  quality  of  workmanship  performed. 


DESCRIPTION. 


(a)  The  searchlight  consists  of  an  old  type  Xa\-y  standard  36-inch  searchlight  made  by  the 
C4eneral  Electiic  Co.,  which  was  part  of  the  equipment  of  the  Maim.  The  lamp  and  ventilating 
hood  were  removed  from  this  drum  and  a  new  ventilating  hood,  containing  a  blower,  was  placed 
on  the  drum.  Ventilating  ducts  were  supplied  and  installed  on  the  inside  of  the  drum.  These 
carry  the  draft  from  the  old  ventilating  outlets  in  the  base  of  the  drum  up  to  the  top  of  the  drum 
near  the  ventilating  blower.  A  new  lamp  housing  was  supplied,  the  old  housing  removed,  and  the 
new  housing  installed  in  its  place.  A  metal  box  containing  ammeter,  thermostat,  negative  feed- 
ing rheostat,  and  finder  was  also  supplied.  The  drum  was  pierced  for  the  finder  and  thermostat 
and  the  box  mounted  on  the  drum.  A  mirror  for  focusing  the  crater  image  onto  the  thermostat 
strips  was  furnished  and  mounted  within  the  drum.  The  tracks  used  for  holding  the  old  lamp  in 
place  were  altered  to  fit  the  new  lamp. 


60 


THE   SEARCHLIGHT. 


(5)  The  lamp  consists  of  the  standard  Sperry  mechanism,  being  of  the  indirect  air-cooled 
type  and  similar  in  every  way  to  that  described  in  machinery  division  test  report  Xo.  202,  with 
the  exception  that  the  diameter  of  the  positive  carbon  is  J  in.stead  of  J  inch,  and  the  operating 
mechanism  is  designed  for  120  amperes  instead  of  150  amperes. 

(c)  The  front  door  was  altered,  having  a  hole  cut  in  the  glaas  and  a  carbon-holder  tube  mounted 
out  in  front  for  retaining  the  positive  carbon. 

TESTS. 

(al  Testa  were  conducted  on  the  lamp  to  determine  the  operation,  carbon  consumption, 
temperatures,  etc.,  and  data  taken  for  the  various  candlepower  determinations  and  spectrum 
analysis  of  the  arc  and  beam. 


Kl'J.  42. 
RESULTS. 

(o)  Operation. — The  lamp  was  burned  continuously  for  a  period  of  seven  hours  and  operated 
perfectly  for  this  period,  gi\-ing  no  trouble  and  requiring  no  attention  from  the  operator. 

(6)  Temperature. — Temperature  readings  were  taken  on  the  various  parts  of  the  dru.m  with 
the  lamp  operating  under  normal  conditions.  The  shutter  was  then  closed  for  a  period  of  two 
minutes,  at  the  end  of  which  time  temperatures  were  noted  and  found  as  follows: 


Shutter. 

Exhaust. 

Drum 
sides. 

Mirror. 

Room. 

Shutter. 

Open 

'C. 
M.5 
58.2 

•c. 

55.0 
58.8 

'C. 

51 
57 

•c. 

28 
28 

°C. 

55.9 

THE   SEARCHLIGHt. 

(c)  Carbons. — The  carbon  details  for  this  lamp  are  as  follows: 


61 


Diameter.      Length. 


Positive.. 
Negative. 


MiUimrter. 
13 
11 


India. 


36 
13 


(d)  Carbon  consumption. — The  carbon  consumption  is  about  4  parts  of  positive  to  1  part  of 
negative  by  length,  a  trim  lasting  about  2}  hours. 


Fig.  4.3. 

(«)  Candkpower. — The  lamp  was  removed  from  the  drum  and  readings  taken  of  the  total  hori- 
zontal candlepower  through  an  angle  of  180°,  the  results  of  which  are  shown  in  figure  42. 

(/)  Readings  were  then  taken  to  determine  the  crater  intensity,  which  was  found  to  be  a 
maximum  at  20°  (fig.  4.3).  The  maximum  ratio  of  crater  light  to  total  light,  however,  figures  out 
at  10°  and  is  73  per  cent  at  this  angle  and  shows  56.5  per  cent  of  the  total  at  the  standard  40°  angle. 
The  crater  and  carbon  tips  comprising  the  light  source  within  a  sphere  of  a  diameter  equal  to  the 
positive  crater  diameter  shows  79  per  cent  of  the  total  light  at  0°  angle  and  60.4  per  cent  of  the 
total  light  at  40°  angle.     The  results  of  the  above  are  shown  in  figures  42,  43,  and  44. 

(g)  Intrinsic  brilliancy. — The  average  intrinsic  brilliancy  of  the  crater  of  the  positive  carbon 
is  equal  to  the  area  of  the  positive  crater  divided  into  the  mean  spherical  candlepower  of  the  crater, 


62 


THE  SEABCHLIGHT. 


which  is  found  from  curve  4,  inclosure  (C),  to  be  25,000  candlepower.     The  diameter  i>f  tlie  crator 

is  10  milliineters.  c^\-ing  an  area  of  78.54  square  millimeters,  which  gives-  - 

(M.  S.  C.  P.)<:     25.500     .,..         ,,  ....      , 
T '  =  .r^-rz=^-'^  candlepower  per  square  iiiilhuieter 

as  the  average  intrinsic  brilliancy  of  the  crater  only. 

(A)  Current  density. — The  current  density  of  the  crater  only  is  equal  to  the  total  amporo  ciir- 

I  120 

rent  divided  by  the  area  of  the  crater,  which  is  t"  =  70^  =  1-53  amperes  per  square  millimetor 

as  an  average  current  density  for  the  crater. 


FlQ.  44. 

(i)  Total  light  on  mirror. — The  light  useful  on  the  mirror  expressed  in  lumins,  is  equal  to  the 
S3lid  angle  subtended  by  the  mirror,  multiplied  by  the  M.  S.  C.  P.  of  the  useful  light  source     The 
M.  S.  C.  P.  is  found  from  figure  4f>  to  be  .S5,500  candlepower  which  gives 
Lumins  on  mirror  2  7r(l-Co8l)X38.500 
Lumins  on  mirror  6.28X0.5f>5X3S.500=137,00O. 
(j)  Efficiency  0/  mirror  ani  front  door. — The  average  efficiency  of  the  mirror  and  glass  door  of 
the  searchlight  is  about  60  per  cent. 

(t)  Lumins  in  beam  outside  front  of  glass. — The  total  light  in  the  beam  just  outside  the  front 
door  is  the  total  lumins  on  miiTor  multiplied  by  the  efficiency  of  mirror  and  front  door  which  gives 

137,000X0.00=90,500. 
This  total  value  covers  an  area  equal  to  the  area  of  front  door,  which  when  divided  by  this  area 
gives^ 

Lumins    90,500    ,„  _„ 
A      =  7.08  =12,760 

lumins  per  square  foot  at  the  front  door  of  the  searchlight. 


THE   SEAECHLIGHT.  63 

(J)  Range. — Considering  for  Xew  York  and  vicinity  an  atmospheric  absorption  of  10  per  cent 
per  3,000  feet  for  average  weather  conditions,  this  gives  an  illuminant  of  81, .500  lumins  total  on  the 
target  at  about  3,000  feet.  The  dispersion  of  the  beam  of  this  light  is  about  54  each  side  of  the 
horizontal,  giving  a  total  dispersion  of  1°  48",  which  gives  a  diameter  of  100  feet  at  3,000  feet  from 
the  hght.  This  gives  an  area  of  about  7,850  square  feet,  gi\lng  an  average  illumination  of  10.4 
lumins  per  square  foot  at  3,000  feet.  This  figures  about  20  lumins  per  square  foot,  at  2,400  feet. 
This  checks  very  closely  mth  the  average  illumination  on  a  target  2,400  feet  away,  using  the  150. 
ampere  high-power  arc.  There  is  a  difference,  however,  as  the  150-ampere  arc  has  a  greater  dis- 
persion, thus  giving  a  larger  illuminated  area  at  the  same  distance  from  the  Ught.  The  effective 
range  of  this  Ught  should  therefore  be  very  nearly  the  same  as  the  150-ampere  searchlights  of  the 
same  manufacturer,  but  the  area  covered  by  the  beam  will  be  less. 

{m)  Color  characteristics.— From  curves  the  following  distribution  of  the  visible  spectrum  has 
been  determined: 


Color. 

Wave  length 
in  micron.s. 

Per  cent 
in  arc. 

Per  cent 
in  beam. 

Violet  and  blue 

tJp  to  0.502 
0.  .502  to    .560 
..560  to    .592 
.59210    .614 
.614  to    .660 

5.1 
.15.3 
27.0 
16.85 
15.75 

.5.37 
42.6 
28.2 
14.0 

9.83 

Yellow                 .                

Ro.1                                   

The  above  results  show  nearly  the  same  characteristics  of  beam  color  and  arc  spectrum  dis- 
tortion as  the  loO-ampere  36-inch  lamp.  This  arc  shows  a  slightly  lower  transmission  efficiency 
than  the  150-ampere  lamp,  due  probably  to  a  large  quantity  of  red  Ught  which  appears  in  the  arc 
spectrum,  and  to  the  transmission  of  which  the  mirror  and  front  door  are  not  very  efficient. 

CO.VCLUSION-. 

(a)  The  workmanship  on  the  present  converted  Ught,  although  crude,  is  effective,  as  the  Ught 
operates  properly  and  steadily. 

(6)  .'Vs  compared  with  the  old  type  of  Ught,  this  remodeled  Ught  is  superior  in  every  way.  As 
compared  with  the  regular  150-ampere  high-power  Ught,  this  Ught  is  sUghtly  less  effective,  o\ving 
to  the  smaller  area  covered  by  the  beam. 

(c)  It  is  considered  that  the  change  of  all  low-power  Ughts  can  be  accompUshed  by  the  ships 
personnel  in  the  same  way  as  the  present  conversion  was  accompUshed,  pro\'ided  that  manufac- 
turers be  required  to  furnish  a  complete  and  detailed  instruction  sheet,  explaining  thoroughlj'  all 
the  operation,  instaUation,  and  adjustment  features  of  all  parts  of  the  searchUght. 

THE  75-AMPERE  .4RC  FOR  24.INCH  fflGH-INTENSITY  SEARCHLIGHTS. 

In  providing  a  high-intensity  arc  for  use  in  searchlights  of  sizes  smaller 
than  the  36-inch  searchlight,  it  has  been  found  necessary  to  develop  a  high- 
intensity  arc  of  lower  amperage. 

The  behavior  of  the  high-intensity  arc  changes  radically  vrith  changes  in 
amperage.  For  instance,  it  has  been  foimd  that  it  is  practically  impossible 
to  obtaia  the  high-intensity  arc  phenomena  at  any  current  below  65  amperes. 

This  places  a  limit  to  the  extent  to  which  the  arc  may  be  reduced  in  cur- 
rent consimiption.  At  the  same  time,  however,  many  other  characteristics 
of  the  arc  change  at  this  lower  limit  of  usefulness,  which  make  it  necessary  to 
rearrange  the  electrodes  and  change  the  normal  burning  conditions. 

The  accompanying  diagram  (fig.  47)  of  the  75-ampere  arc  shows  the  many 
points  of  difference  between  it  and  the  150-ampero  arc.  It  will  be  noticed 
that  the  arc  length  is  extremely  short,  the  normal  length  being  only  about 


64 


THE  SEARCHLIGHT. 


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FIG.   48.- SPERRY    24-INCH     HIGH     POWER    SEARCHLIGHT.     RIGHT    SIDE.     90°    ELEVATION. 


THE   SEARCHLIGHT. 


65 


one-fourth  inch.  The  negative  electrode,  however,  is  tilted  at  an  angle  of 
45°  to  the  positive  and  the  tip  burns  slightly  below  the  positive  crater,  so  that 
even  with  the  short  arc  the  negative  casts  practically  no  shadow  on  the  mirror. 

The  reason  for  the  short  arc  and  steep  angle  of  the  negative  is  that  the 
negative  arc  flame  at  75  amperes  does  not  have  the  same  velocity  and  force 
that  is  characteristic  of  the  150-ampere  arc.  Consequently,  a  long  arc  at  75 
amperes  is  very  unsteady  and  flickers  badly. 

The  negative  electrode  is,  therefore,  tipped  at  a  steep  angle,  which  causes 
the  arc  flame  to  issue  from  it  vertically.  As  is  well  kno^vn,  a  vertical  arc  flame 
is  much  steadier  than  a  horizontal  arc.     The  positive    carbon    is,  however, 


Appearance    of  Arc 
75  Amperej 
^5  Volts 


Carhror) 


C<vr\xot) 


negative 


Fio.  47. — Arc  of  Sperry  2J-iiich  high-pov."cr  searchlight. 

horizontal  and  the  crater  is  brought  into  contact  near  the  base  of  the  vertical 
arc  flame,  thus  insm-ing  a  very  steady  burning  arc  and  at  the  same  time 
increasing  the  light  flux  on  the  mirror  by  the  elimination  of  the 
shadow. 

The  brilliancy  of  the  crater  in  this  arc  runs  as  high  as  550  candlepower  per 
square  millimeter.  This  brilliancy,  although  not  as  great  as  in  the  150-ampere 
arc,  stiU  is  from  three  to  four  times  greater  than  that  of  the  old  standard 
carbon  arc. 

The  color  of  the  searchlight  beam  is  the  same  clear  blue  white  that  is 
distinctive  of  all  the  high-uitensity  searchlights. 

66438—18 ^ 


66  THE  SEABCHLIGHT. 

SPERRY  24-INCH  LAMP  MECHANISM. 

The  75-ampere  arc  used  in  the  24-mch  Sperry  lamp,  for  Navy  use,  admits 
of  a  difTerent  construction  than  that  used  with  the  36-inch  lamp  previously 
described.  Whereas  11 J  Icilowatts  (75  arc  volts  by  150  ampere^  are  consumed 
at  the  arc  of  a  36-inch  lamp,  only  31  kilowatts  (45  arc  volts  by  75  amperes)  are 
consumed  at  the  arc  of  a  24-uich  lamp,  and  consequently  only  one-third  as 
much  heat  has  to  be  dissipated.  This  makes  it  possible  to  operate  the  24-inch 
amp  without  the  use  of  forced  draft  to  cool  the  heads. 

The  general  appearance  of  the  24-incli  lamp  is  shown  in  figure  55.  The 
voltage  control  mechanism  and  the  motor  are  the  same  as  used  in  the  36-mch 
lamp,  except  that  their  windings  are  designed  to  operate  normally  on  45  instead 
of  75  volts. 

The  positive  carbon  is  rotated  and  fed  by  a  pair  of  rollers  which  arc  cut  on 
the  surface  with  a  deep,  sharp,  straight  knurl,  the  teeth  rumiing  parallel  to  tlie 
axis  of  the  roller.  The  rollers  are  mounted  one  above  the  other  with  the  carbon 
in  between.  The  rollers  revolve  iii  opposite  directions,  and  b}'  friction  with 
the  carbon  cause  it  to  revolve  between  them. 

The  motor,  which  runs  normally  at  about  4,200  revolutions  per  minute, 
drives  the  lower  roller  through  a  series  of  worm,  spur,  and  bevel  gears.  A 
sprocket  on  the  lower  roller  shaft  in  turn  drives  the  upper  roller  through  a  chain 
and  sprocket.  These  rollers  are  mounted  in  brackets,  which  are  supported  by 
short  vertical  shafts.  Sprmgs  around  these  vertical  shafts  force  the  rollers 
toward  each  other,  thus  causmg  the  rollers  to  grip  the  carbon.  The  grip  on  the 
carbon  is  released  by  a  lever  at  the  back  of  the  positive  head  which  actuates  a 
cam  for  spreading  the  roUei-s  apart.  The  direction  and  rate  of  feed  of  the 
positive  carbon  is  determmcd  by  the  angle  at  wliich  the  carbon  rollers  are  set. 
When  the  teeth  of  the  rollers  are  parallel  to  the  axis  of  the  carbon,  the  carbon 
rotates  without  advancing  or  retreating.  A  slight  sliift  iu  the  position  of  the 
controlling  handle  on  the  outside  of  the  drum  changes  the  angle  of  the  rollers, 
•the  angle  of  the  upper  roller  being  opposite  to  that  of  the  lower  one,  thereby 
causing  the  carbon  to  slowly  advance  or  retreat.  In  practice,  the  operator 
soon  finds  a  position  for  the  handle  which  gives  a  feed  just  sufficient  to  equal 
the  rate  of  carbon  consumption.  More  rapid  or  slower  feeds  are  required  only 
for  occasional  short  intervals  to  compensate  for  variations  in  carbon  con- 
sumption, due  to  variations  m  current  or  carbon  composition. 

The  current  is  conducted  to  the  positive  by  two  silver-tipped  brushes 
mounted  in  the  forward  part  of  the  licad.  The  head  is  cooled  by  radiation 
from  a  cast-bronze  shield  placed  just  back  of  the  arc.  Air  is  kept  from  the 
carbon  by  a  silica  buslung  whose  flange  is  set  in  asbestos  washers. 

The  negative  feed  is  the  same  as  that  used  on  the  36-mch  lamp,  with  the 
exception  of  the  method  of  releasing  from  the  grip  of  the  rollers.  On  the 
24-mch  lamp  this  is  accomplished  by  a  lever  at  the  rear  of  the  head,  which, 
when  turned  90°  either  way,  causes  a  cam  to  spread  the  brackets  supporting 
the  feed  rollers,  thus  freeing  the  carbon. 


FIG.  49.— SPERRY   24-INCH    HIGH    POWER  SEARCH  LIGHT.      RIGHT   SIDE.     0°   ELEVATION. 

NAMES    OF    PARTS. 


FIG.    50.-SPERRY    24-lNCH     HIGH     POWER    SEARCHLIGHT.    SHOWING     LARGE    ARC     RACK 
USED    ON     ONE    TYPE    OF    LIGHT. 


FIG.    57.-SPERRY    24-INCH     HIGH     POWER    SEARCHLIGHT    WITH     LARGE    ARC     RACK.       RIGHT 
SIDE.     0°    ELEVATION,      NAMES    OF    PARTS. 


FIG.     52.— SPERRY     24-INCH      HIGH      POWER     SEARCH  LIGHI  .    SHOWING     TRIAL     RADIAL     BLIND 

SHUTTER    CLOSED.      FRONT    VIEW. 


FIG.   53— SPERRY   24-INCH    HIGH    POWER   SEARCHLIGHT.    SHOWING    TRIAL    RADIAL   BLIND 
SHUTTER    HALF    OPEN.      FRONT    VIEW. 


J^, 

^ 

«c^ 

FIG.      54.-SPERRY      2*-INCH       HIGH       POWER      SEARCHLIGHT.    SHOWING      VENETIAN      BLIND 
SHUTTER    CLOSED.      FRONT    VIEW. 


FIG.    55.-SPERRY    24-INCH     HIGH     POWER    SEARCHLIGHT    LAMP.      THREE-QUARTER 

BACK    VIEW. 


FIG.  56— SPERRY  24-INCH  HIGH  POWER  SEARCHLIGHT.  FRONT  VIEW  OF  INTERIOR  OF  BAR- 
REL. SHOWING  LAMP  IN  PLACE  AND  SCREEN  TO  PROTECT  MIRROR  FROM  HOT 
PARTICLES. 


FIG.  58.-SPERRY    24-INCH     HIGH     POWER    SEARCHLIGHT.      LEFT    SIDE. 


FIG.    58a.-SPERRY    24-INCH     HIGH     POWER    SEARCHLIGHT,    SHOWING    OPERATOR    ABOUT    TO 

RECARBON    LAMP. 


THE  SEARCHLIGHT.  67 

REMOTE  MECHANICAL  CONTROL  FOR  24-INCH  SEARCHLIGHT. 

The  same  controllers  that  are  used  in  the  remote  mechanical  control 
system  for  the  36-meh  searchlight  are  also  used  for  the  24-inch  light.  The 
mechanism  in  the  base  of  the  lamp  diffei-s  slightly  from  that  in  the  36-inch 
light,  however.  The  controllmg  shafts  again  come  up  through  the  base, 
the  tramhig  shaft  connects  with  the  rack  on  the  moving  part  of  the  base  through 
a  tram  of  gears  and  a  short  piece  of  shaftuig. 

The  elevating  shaft  does  not  come  up  through  the  axis  of  the  base  as  in 
the  case  of  the  36-inch  light,  but  inside  of  the  base  it  is  geared  to  a  piece  of 
shafting  that  does  pass  through  the  axis.  The  upper  end  of  the  shaft  carries 
the  gear  that  engages  the  elevating  rack.  The  pedal  mounted  on  the  side  of 
the  base  engages  or  disengages  both  its  traming  and  elevating  remote  con- 
trols from  the  drum  at  once.  The  mechanism  is  easily  seen  by  removmg  one 
of  the  handhole  covers  from  the  base. 

The  system  of  control  is  essentially  the  same  as  for  the  36-inch  lamp, 
and  provides  the  same  simple  method  of  controlling  the  lamp  from  a  point 
below  it. 


CHAPTEE  5. 
GENERAL  ELECTRIC  CO.  24-INCH    HIGH-POWER  SEARCHLIGHT. 


The  General  Electric  Co.  very  recently  have  perfected  an  air-cooled 
24-inch  high-power  searclilight.  Scarclilights  of  this  type  are  being  supplied 
to  destroyers  and  are  designed  to  meet  the  conditions  of  vibration,  water, 
pitching,  and  rolling  met  with  on  vessels  of  this  type,  and  to  give  good  service 
under  these  severe  conditions. 

Accessibility  of  parts,  water-tightness,  simplicity  of  operation,  and  strength 
are  the  features  particularl}-  emphasized  in  these  searchlights.  A  feature  which 
is  used  in  the  lamps  of  these  scarclJights  is  that  of  forced  ventilation  only, 
rather  than  of  combined  force  and  induced  ventilation  as  used  in  previous 
searcldights.  One  motor  only  is  employed,  and  this  is  mounted  outside  of 
lamp  box,  as  shown  in  illustration.  A  description  of  the  complete  searcldight 
is  given  below. 

The  turntable  has  gear  teeth  cut  around  the  outside  and  is  revolved  on 
tread  rollers,  mounted  on  the  tread-roller  ring,  which  roll  on  a  machined  surface 
on  the  base.     (See  fig.  61.) 

A  pinion  mounted  on  a  vertical  shaft  engages  the  teeth  cut  in  the  perimeter 
of  the  rotating  turntable.  This  pinion  is  driven  through  a  clutch,  directly 
over  the  pinion,  and  is  released  for  free  hand  control  of  the  searchlight  in 
azimuth  by  turning  the  knurled  knob  to  the  left.  The  vertical  shaft,  carrying 
this  pinion,  is  mounted  in  a  bearing  attached  to  the  base  casting.  At  the 
lower  end  of  this  pinion  shaft  is  a  universal  coupling  into  which  the  pipe  running 
to  the  azimuth  controller  is  clasped. 

The  azimuth  scale  and  pointer  indicate  the  movement  of  the  searchliglit 
by  degrees.  Illumination  for  the  scale  is  provided  by  scale  lamp.  By  changing 
the  position  of  the  lever,  at  top  of  lamp  housing,  a  shutter  is  operated  which 
shuts  off  light  from  the  scale.  A  switch  is  mounted  in  the  base  and  tlie  handle 
projects  through  the  support  on  the  base,  the  on  or  off  position  being  indicated 
by  small  plates.  (See  fig.  62.)  Cables  run  from  the  switch  in  the  base  to  con- 
nection strips  on  the  contact  rings.  The  contact  rings  are  carried  on  insulation 
blocks  secured  to  the  top  of  the  base,  as  shown  in  figure  61.  Plungers  mounted 
on  an  insulation  piece  in  the  plunger  box  project  through  the  turntable  and 
bear  on  the  contact  rings.  From  the  plunger-box  cables  also  run  up  the  arms 
to  the  switch  on  the  barrel  and  to  the  plug  which  connects  with  the  receptacle 
on  the  lamp. 

Arms  mounted  on  the  turntable  carry  the  barrel  on  trunnion  pins. 

The  vertical  training  rack  is  bolted  to  the  right-hand  trunnion  block  and 
is  driven  bj^  a.  pinion  connected  through  bevel  gearing  and  shafts  to  the  uni- 
versal coupling  at  center  of  base.     A  pipe  clamps  to  the  lower  end  of  this 
68 


THE   SEAKCHUGHT. 


69 


/ 


-A 


Fio.  59.— O.  E.  24-lnoh  high-power  ssarehllght.    Slde^riew. 


70  THE   SEARCHUGHT. 

universal  eontroUor  and  runs  to  the  elevating  controller.  Stops  on  the  end 
of  the  vertical  traininj;  rack  limit  the  travel  of  the  barrel  to  100°  elevation 
and  30°  depression.  Free  hand  control  of  the  elevation  and  depression  of  the 
barrel  may  bp  obtained  bv  unscrewing  the  starwheel  on  the  right-hand  arm. 
The  altitude  scale  and  pointer  indicate  the  elevation  or  depression  of  the  barrel 
in  degrees.  Illumination  is  provided  in  the  same  manner  as  described  in  the 
case  of  the  azimuth  scale. 

The  front  and  rear  rings  are  grooved  to  receive  the  inner  and  outer  sheets 
of  the  barrel  and  are  held  together  by  side  rods  which  carry  the  trunnion 
blocks.  Eyebolts  are  screwed  into  the  front  and  rear  rings  in  each  side  for 
lifting. 

A  hinged  door  is  provided  for  access  to  the  interior  of  barrel. 

The  mirror  is  mounted  in  miiTor  frame  secui'ed  to  the  rear  ring  and  is 
held  in  place  by  clips.  Sheet  asbestos  is  placed  on  the  front  and  back  of  the 
mirror  where  it  rests  on  the  frame  and  asbestos  rope  is  packed  around  the 
edge.  The  mirror  with  its  entire  mounting  may  be  jemoved  from  the  barrel 
by  turning  the  six  latches  on  the  rear  ring. 

Peep  sights  of  dark  ruby  glass  on  both  sides  of  the  barrel  permit  viewing 
the  arc.     Swinging  covers  protect  the  glass. 

An  arc  image  screen  described  under  ".Vrc  image  system"  is  mounted 
on  the  barrel. 

The  fuse  box  has  a  lunged  water-tight  cover,  which  is  held  closed  by  a 
winged  screw.  Two  General  Electric  catalogue  34952  10-ampcre  fuses  are 
used. 

The  switch  box  is  mounted  on  the  barrel  on  a  rod  between  the  front  and 
rear  rings.  The  switch  box  cover  is  screwed  to  the  box  and  is  water-tight. 
The  handle  of  the  switch  projects  through  the  stufluig  tube  in  the  cover  and 
the  on  and  ofi'  positions  are  indicated  by  small  plates. 

The  thermostat  is  contained  in  the  thermostat  l>ox  mounted  on  the  right- 
hand  side  of  the  barrel.  This  is  fully  described  under  thermostat  and  arc 
image  sj-stem. 

All  geare  are  inclosed  with  covers  to  prevent  injury  to  operator,  and  oil 
holes  are  provided  as  described  under  oihng. 

The  signaUng  shutter  is  of  the  venetian-blind  type  and  is  operated  by  a 
handle  on  tlie  side  and  returned  to  the  closed  position  by  a  spring.  The  shutter 
may  be  removed  by  unscrewing  the  bolt  with  handle  located  at  bottom  of  the 
shutter  and  lifting  up. 

A  sighting  tube  is  mounted  on  the  right-hand  side  of  the  barrel  above 
the  thermostat  box,  and  consists  of  a  brass  tube  with  small  sighting  hole  in 
one  end  and  cross  wires  in  the  other  end. 

The  ventilator  is  made  of  sheet  brass  and,  while  light-tight,  provides  an 
exit  for  the  air  and  gases  from  the  barrel. 

The  lamp  trough  is  bolted  to  the  bottom  machined  surfaces  of  the  front 
and  rear  rings  and  supports  the  lamp.  Bolted  to  the  trough  is  the  fan  hous- 
ing, which  contains  a  fan  driven  by  a  motor.  The  motor  is  secured  in  the 
motor  compartment,  which  is  mounted  on  the  rod  between  the  front  and  rear 
rings.  The  fan  rotates  in  the  fan  housing  and  delivers  air  to  the  barrel,  and 
through  the  air  connection  to  the  lamp,  as  described  under  "Air  circulation." 


THE  SEAKCHUGHT. 


71 


Fig.  60.— G.  E.  24-iiich  higli-po  er  searclUight.   Front  view. 


72  "FHE   SEAHCHLIOHT. 

Tliis  nir  connection  may  be  disconnected,  when  changing  the  lamp,  by  pulUng 
out  knurlocf  knob  and  giving  it  a  quarter  turn. 

On  the  end  of  the  motor  sliaf  t  opposite  the  fan,  a  worm  and  gear,  inclosed 
in  gear  box,  drives  through  a  universal  joint,  a  coupUng  which  is  connected  to 
the  lamp  and  which  drives  the  lamp  mechanism.  On  the  outer  end  of  this 
driving  shaft  is  a  handle  with  latch  which  releases  the  motor  drive  and 
allows  tlie  driving  shaft  to  bo  rotated  by  hand. 

There  are  two  coTmection  plugs,  one  for  the  main-hne  circuit  to  the  lamp 
and  the  other  for  the  wires  connecting  the  thermostat  to  the  lamp.  These  arc 
arranged  so  that  it  is  impossible  to  insert  the  plugs  except  in  the  correct  posi- 
tion.    The  cables  arc  brought  into  the  plugs  through  stuffing  tubes. 

Inside  the  barrel  is  a  niirror  guard,  which  swings  under  the  arc  in  all 
positions  of  the  barrel  and  protects  the  mirror  from  hot  particles  that  may  fall 
from  the  carbons.     This  guard  is  insulated  from  the  barrel. 

An  incandescent  carboning  lamp  is  provided  on  the  inside  of  the  barrel. 
Hush  with  tlie  inner  sheet,  to  provide  illumination  of  the  barrel  when  install- 
ing new  carbons  in  the  lamp  or  making  any  adjustments. 

The  iris  shutter  is  operated  by  a  handle  and  when  closed  shuts  oil  all 
liirht.  The  shutter  is  mounted  in  the  same  frame  as  the  front  door  and  may 
be  removed  with  the  door  by  pressing  down  on  latch  above  the  right-hand 
handle  and  rotating  the  shutter  ring  counterclockwise  about  5°.  The  front 
door  glass  strips  may  bo  removed  separately,  being  held  in  place  by  retaining 
strips.  The  front  door  is  provided  with  reinforcing  strips  to  prevent  injury 
due  to  gunfire.  A  carbon  tube  with  liinged  cover  provides  an  entrance  for  the 
positive  carbon. 

The  focusing  screw  at  rear  of  lamp  trough  permits  the  adjustment  of  lamp 
in  focus  as  described  under  "  opek.\tio\." 

VENTILATION  SYSTEM. 

(See  fig.  64.1 

The  barrel  has  imier  and  outer  sheets,  the  lower  quadrants  on  either  side 
of  the  lamp  trough  being  closed  at  the  top  by  the  inner  sheet  joining  the  outer. 
Air  from  the  fan  housing  enters  between  the  inner  and  outer  sheets  at  the 
front  of  the  barrel.  On  the  right-hand  side  the  air  passes  between  the  two 
sheets,  part  entering  the  air  connection  to  the  lamp  and  the  remainder  pass- 
ing through  small  openings  in  the  rear  ring  to  a  recess  in  the  mirror  frame, 
which  runs  on  each  side  approximately  100°  from  the  bottom  vertical  center 
line.  On  the  left  side  the  air  passes  between  the  inner  and  outer  sheets  and 
through  large  holes  in  the  rear  ring  to  the  same  recess  in  the  mirror  frame. 
Slotted  air  passages  connect  this  recess  to  the  front  of  the  mirror  frame  and 
a  part  of  the  air  flows  through  these  slots  and  over  the  face  of  the  mirror, 
cooling  it  and  preventing  the  deposit  of  the  combustion  products  of  the  car- 
bons on  the  mirror.  This  air  is  then  exhausted  through  the  top  ventilator. 
The  remainder  of  the  air  flows  over  the  back  of  the  mirror  into  a  recess  in  the 
-upper  portion  of  the  min-or  frame,  from  which  it  passes  through  openings  in 
the  upper  part  of  the  rear  ring  to  the  upper  quadrants  of  the  space  between 
the  inner  and  outer  sheets  of  the  barrel.  The  air  then  flows  do\vnward  to 
the  center  of  the  barrel  and  out  t»hrough  openings  between  the  inner  and  outer 


HG.  62.— UNDER    SIDE    OF    BASE    FfcOJECIOR. 


THE    BEAKCHLIGHT. 


73 


sheets  on  each  side  to  the  interior  of  the  barrel,  where  it  is  exhausted  through 
the  top  ventilator. 

.UlC-IMAGE  AND  THERMOSTAT  SYSTEM. 

(See  fig.  63.) 
ARC-IMAGE   SYSTEM. 

In  the  arc-image  system  light  rays  from  the  arc  at  A  are  passed  through 
the  lenses  E,  F,  and  G  and  reflected  on  the  frosted-glass  screen  H,  which  is 
located  on  the  right-hand  side  of  the  barrel  toward  the  rear. 

ARRANGEMENT 

or 
THERMOSTAT 

ARC  image:  system. 


To  POilTlve 

rccp  MAGAfer 


Fig.  6.f. 

A  fuU-size  upright  image  of  the  arc  is  produced  on  the  screen  H  and  a 
black  line  marked  on  the  glass  indicates  the  correct  position  for  the  end  of  the 
positive  carbon  when  it  is  at  the  focal  point  of  the  searchhght  mirror. 

The  three  lenses  E,  F,  and  G  are  moimted  in  a  lens  holder  and  form  a 
unit  known  as  the  lens  tube. 

Over  the  frosted-glass  screen  H  is  a  swinging  cover  which  can-ies  a  dark 
ruby  glass  to  reduce  the  intensity  of  the  image  of  the  screen  H  when  operating 
the  searchligiit  at  night. 

THERMOSTAT    SYSTEM. 

Light  and  heat  rays  from  the  arc  at  A  pass  through  the  lens  B  and  fall 
upon  the  mirror  C,  where  they  are  reflected  and  converged  on  the  plane  of 
the  thermostat  strips  D-1  and  D-2. 


74 


THE  SEARCHLIGHT. 


When  the  end  of  the  positive  carbon  is  in  the  exact  focus  of  the  mirror 
the  spot  at  which  the  light  and  heat  rays  are  concentrated  is  just  off  the  ther- 
mostat strip  D-1. 

As  the  carbon  burns  away  this  spot  moves  onto  the  thermostat  strip  D-1, 
causing  it  to  operate  and  move  the  contact  lever  D-3  into  contact  with  D-5. 
This  closes  the  circuit  to  the  positive  feeding  magnet. 

The  thermostat  strip  D-2,  contact  lever  D-4,  and  contact  D-6  are  au.xili- 
arics  and  are  called  into  operation  onlj'  upon  failure  of  D-1,  D-,3,  and  D-5 
to  operate. 

A  switch  D-7  permits  the  thermostat  control  of  the  positive  feed  to'  be 
cut  out.  The  handle  of  this  switch  extends  th.rough  the  thermostat  ])ox  and 
is  operated  from  the  outside,  there  being  off  and  on  indications  on  the  ther- 
mostat box. 

The  adjustments  of  the  thermostat  arc  carefully  made  at  the  factory  and 
sliould  not  be  disturbed  unless  there  has  been  some  mechanical  injury  of  the 
thermostat. 


Flo.  64.— Ventilation  diagram  of  G.  E.  24-inch  high-pov  cr  searchlight. 


CONNECTIONS. 


DESCRIPTION   OF   CmCUITS. 

[Sec  fig.  Go.] 

Main  lamp  circuit.  — ^Thc  generator  is  connected  to  the  switch  in  the  base, 
the  positive  line  being  connected  to  the  rheostat  so  that  the  current  passes 
througli  the  rheostat.  From  the  switch  in  the  base,  the  circuit  runs  tlirough 
the  contact  rings,  to  the  contact  plungers,  to  the  switch  on  the  barrel,  to  the 
connection  i>lug,  to  the  receptacle  in  lamp,  to  the  carbons,  the  positive  side 
passing  through  the  striking  magnet. 

The  azimuth  scale  lamp  circuit  is  connected  to  the  contact  rings.  The 
altitude  scale  lamp  circuit  is  conne -ted  to  the  contact  plungers. 

The  carboning  lamp  and  ventilating  motor  circuits  are  connected  to  the 
switch  on  the  barrel  through  the  fuses. 

One  side  of  the  thermostat  circuit  is  connected  to  the  positive  main  lamp 
receptacle,  and  passes  through  the  positive  feeding  magnet  to  the  thermostat 


FIG.  65.— LAMP.     G.  E.  24'  H.  ?.  SEARCHLIGHT 


THE   SEAECHLIGHT. 


75 


receptacle.  The  plug  which  enters  this  receptacle  is  connected  by  one  of  the 
conductors  of  twin  conductor  cable  to  one  contact  on  the  thermostat.  The 
other  contact  is  connected  through  the  switch  in  the  thermostat  box  and 
through  the  other  twin  conductor  cable  to  the  plug  and  from  the  plug  to  recepta- 


"^^^'5 
^^^^=^^1 


a 


8 


.1 

5 


cle  in  lamp.  This  receptacle  is  connected  to  the  negative  main  lamp  receptacle. 
The  common  point  of  the  negative  feeding  clutch  coils  is  connected  through 
the  clutch  switch  to  the  negative  main  lamp  receptacle.  The  other  ends  of 
the  coils  are  connected  through  tiie  contact  points  on  the  relay  to  the  positive 
side  of  the  circuit  at  the  striking  magnet. 


76  THE  SEARCHLIGHT. 

OnjNO. 

Bowen  oilers  are  provided  as  follows: 

Four  on  top  of  turnta1)lo  for  oiling  the  tread  rollers. 

One  in  the  ])racket  for  pinion  mesbing  with  the  turntable,  oiling  the  shaft 
to  the  universal  coupling. 

One  on  gear  cover  at  center  of  turntable  for  oiling  center  pin. 

TNvo  on  bearing  on  turntable  for  oiling  vertical  traming  shaft. 

One  on  bearing  on  arm  for  oiling  vertical  training  shaft. 

One  on  arm,  behind  scale  lamp,  for  oiling  shaft  driving  vertical  training 
pinion. 

One  on  top  of  each  arm  for  oiling  trunnion  pin. 

Grease  cup  is  placed  on  end  of  gear  casing  on  motor  compartment  for 
lubricating  worm  and  gear. 

Two  oil  tubes  leading  to  the  motor  bearings  are  directly  under  plugs  (one 
largo  and  one  small)  on  the  u])pcr  side  of  the  motor  compartment.  It  is 
necessary  to  remove  these  plugs  in  oihng  the  motor. 

The  large  gear  on  turntable  and  the  vertical  training  rack  should  occasion- 
ally be  lightly  coated  with  vaseline. 

LAMP. 

Rating. — The  lamp  operates  at  7.5  amperes  and  approximately  60  volts  at 
the  arc,  the  difTereiice  between  the  line  and  arc  voltage  being  absorbed  in  the 
supply  leads  and  the  rheostat  which  is  in  series  with  the  arc.  The  voltage 
rating  is  given  appro.Kimately,  as  the  lamp  is  controlled  by  a  cun-ent  relay 
described  later  and  which  tends  to  maintain  a  constant  current  arc. 

Carbons. — The  positive  carbon  is  11  millimeters  (approximately  -^  inch) 
diameter,  24  inches  long.  The  negative  is  11  millimeters  diameter,  8 J  inches 
long. 

The  positive  carbon  has  a  soft  core  and  bums  with  a  deep  crater. 

The  nccative  carbon  has  a  small  core  of  harder  material  than  the  core  of 
the  positive  carbon. 

Copfcr-plated  carbons  should  not  he  used  in  this  lamp. 

Cai-boning. — Insert  the  positive  carbon  so  that  it  projects  i  inch  from  the 
end  of  the  positive  carbon  nose. 

The  negative  carbon  should  then  be  inserted  to  project  about  J  inch  from 
the  end  of  the  negative  nose.  It  is  not  necessary  that  the  negative  carbon  touch 
the  positive  in  carboning  the  lamp. 

General  features. — The  ventilating  motor,  in  addition  to  rotating  the  fan, 
drives  the  lamp  mechanism  as  described  above.  The  positive  carbon  is  rotated 
and  fed  toward  the  mirror.  The  negative  carbon  does  not  rotate  but  is  fed 
forward  and  back  to  maintain  essentially  a  constant  current  at  the  arc. 

When  the  lamp  is  not  burning,  the  negative  carbon  is  held  against  the 
po3itive  by  a  spring  attached  to  the  arm  carrying  the  negative  head.  ^Vhen 
the  switch  is  closed,  current  passes  through  the  starting  magnet,  which  draws 
the  arc  down,  separating  the  carbons  and  establishing  the  arc. 

A  relay  contact  arm,  attached  to  one  of  the  yokes  of  the  startmg  magnet, 
as  shown  on  figure  66,  operates  on  leakage  flux,  and  floats  between  two  contacts 
when  the  arc  current  is  normal.     On  an  excess  arc  current  the  arm  makes 


ill 


FIG.  67.-LAMP.     G.    E.  24"   H.    P.   SEARCHLIGHT. 


FIG.   69— NEGATIVE     HEAD       G.    E.   24"    H.    P.    SEARCHLIGHT. 


wnub     uuuuw 


^ 


'.^m^i^tm 


1  r: 


0~ 


t^ 


¥ 


FIG.    71,      POSITIVE     ROTATING     MECHANISM.     G.   E.  24"   H.   P.   SEARCHLIGHT. 


THE   SEAECHLIGHT.  77 

contact  with  the  lowei"  contact  to  one  of  the  negative  feed  clutch  coils,  energizing 
the  coU  and  throwing  the  clutch  into  the  feed  apart  position.  This  moves 
the  negative  carbon  away  from  the  current  to  normal,  when  the  relay  arm 
will  again  float  between  the  two  contacts,  opening  the  circuit  to  the  clutch 
magnet  and  releasmg  the  backward  feed. 

If  the  current  is  below  normal,  due  to  bm-ning  away  of  the  carbons,  the 
relay  contact  arm  makes  contact  with  the  upper  contact,  closmg  the  circuit 
to  the  upper  contact  which  is  connected  to  the  other  negative  feed  clutch  coil. 
This  thi-ows  the  clutch  into  the  feed-together  position  and  feeds  the  negative 
carbon  ahead  imtil  the  arc  current  rises  to  normal  and  the  relay  contact  arm 
again  floats. 

In  this  connection  note  that  when  no  current  is  passing  through  the  starting 
magnet  and  carbons,  the  relay  contact  arm  is  against  the  upper  contact  in 
the  feed-together  position  so  that  when  the  main  switch  is  closed  the  negative 
carbon  will  feed  ahead  imtil  it  touches  the  positive  carbon. 

The  positive  carbon  is  fed  in  one  direction  only,  toward  the  mirror,  the 
feeding  being  regulated  by  the  thermostat,  as  described  xmder  the  arc  image 
and  thermostat  system. 

Levei-s  on  the  rear  end  of  the  lamp  frame  have  dial  plates  marked  "A" 
at  the  bottom  of  each  plate.  This  indicates  the  position  of  the  lever  for  auto- 
matic feed. 

Graduations  on  these  dials  mark  the  position  of  the  levers  for  hand  feed. 
Moving  the  lever  up  the  scale  increases  the  rate  of  feed. 

The  automatic  positive  feed  is  cut  out  by  opening  the  switch  on  the  ther- 
mostat box.  Moving  the  negative  feed  lever  to  the  hand  feed  positions  opens 
a  switch  to  the  negative  feed  clutch  coils. 

The  searchlight  lamp  is  shown  in  figures  66,  67,  and  68,  and  consists 
essentially  of  means  for  supporting  positive  and  negative  carbons  at  the  center 
of  the  barrel,  and  mechanism  for  feeding  the  carbons  in  the  proper  ratio. 

The  positive  carbon  is  rotated  to  prevent  mieven  burning  of  the  carbon 
caused  by  the  rising  arc  stream.  The  rotating  mechanism  is  showTi  assembled  in 
figure  71  and  the  parts  in  figure  72.  The  carbon  is  held  between  two  toothed 
rollers  of  hardened  steel  with  wide  grooves  cut  in  their  faces  to  insure  a  grip 
on  the  carbons  for  rotating.  The  roUers  are  pinned  to  shafts  which  have  spur 
gears  fastened  to  the  end.  These  gears  engage  with  one  another.  A  worm 
gear  is  pinned  to  the  end  of  one  shaft  and  is  driven  by  a  worm  on  a  shaft  par- 
allel to  the  axis  of  the  carbon.  There  is  a  star  wheel  fastened  to  the  shaft 
which  engages  with  a  pin  on  the  feeding  rod.  This  star  wheel  rotates,  with  the 
feeding  gears  and  rollers,  about  the  axis  of  the  carbon  and  during  each  revo- 
lution is  advanced  by  coming  into  contact  with  the  pin  on  the  end  of  the  feeding 
rod  if  the  rod  is  in  the  feed  position. 

Advancing,  the  star  wheel  rotates  the  geai-s  and  rollers,  feeding  the  carbon 
ahead.  All  of  the  positive  rollers,  gears,  and  shafts  are  moimted  in  two  bearing 
arms  which  are  pivoted  on  the  shell  sliowoi  in  the  lower  left-hand  corner  of 
figure  72,  and  are  pressed  against  the  carbon  by  two  "U  "  springs.  The  shell 
is  rotated  on  the  outer  tube  by  means  of  the  bevel  gear  on  the  shell  and  bevel 
pinion  rotating  in  the  end  bearing  driven  by  the  positive  rotating  shaft.  This 
outer  tube  is  clamped  in  the  end  bearing  by  means  of  a  hexagon  nut.    Inside 


78  THE    SEAECHUGHT. 

of  the  outer  tube  is  the  inner  tube,  which  can  be  pushed  forward  by  means  of 
the  lever  shown  in  tlie  lo\ver  riglU-hand  corner  of  fiojure  72,  Hfting  the  rollers 
from  the  carbon  by  forcing;  apart  the  bearing  arms.  The  end  bearing  is  fastened 
to  one  end  of  the  cage  shown  in  figure  72,  and  the  other  end  is  screwed  to  the 
casing,  being  insulated  from  it.  The  casing  incloses  the  radiator,  which  has  a 
slot  in  the  top  for  the  silver  contact.  The  contact  is  pressed  against  the  carbon 
by  a  spring  acting  on  the  contact  lever  pivoted  on  the  shell.  The  contact  is 
lifted  by  pressing  down  the  handle  on  lever  at  rear.  This  also  spreads  the 
rollers  as  described  above.  On  the  front  of  the  casing  is  mounted  the  obdurator, 
which  holds  in  place  the  positive  nose.  The  obdurator  prevents  direct  light 
from  the  arc  passing  througli  the  front  door  and  also  acts  as  a  heat  shield  for 
the  rotating  mechanism.  The  casing  has  an  opening  in  the  bottom,  allowing 
air  to  pass  over  the  vanes  of  the  radiator  and  through  the  rectangular  oi)cning 
in  the  top,  to  be  exhausted  i)y  the  ventilator  in  the  barrel.  The  casing  is  secured 
to  and  insidated  from  tlic  support  shown  in  hgure  74,  which  is  hollow,  to  give 
passage  to  the  air. 

The  negative  head  is  shown  assembled  in  figure  69  and  the  parts  in  figure  70. 

The  carbon  is  held  between  toothed  rollers  of  hardened  steel,  pinned  to 
shafts  which  have  worm  gears  fastened  to  one  end.  On  the  other  end  are  fas- 
tened smooth-faced  rollers.  Meshing  with  the  worm  gears  are  a  right  and  left 
hand  worm,  driven  by  the  negative  feeding  shaft  through  a  universal  coupling. 
The  rollers,  gears,  and  shafts  are  mounted  on  bearing  arms,  pivoted  on  the 
negative  head  casting,  and  the  rollers  are  held  against  the  carbon  by  means  of 
compression  spring  at  the  rear  end.  The  negative  nose  is  held  in  place  by  a 
punching  which  is  screwed  to  the  body  casting.  The  radiator  supports  the 
bottonr  silver  contact  and  is  screwed  to  the  bodj'  casting.  The  upper  silver 
contact  is  held  against  the  carbon  by  the  contact  lever  pressed  by  a  spring  at 
the  extreme  roar  end.  The  lever  is  lifted  by  means  of  a  cam  on  the  lever  with 
two  handles,  and  it  also  forces  the  tapered  pin  between  the  smooth  rollers  on 
the  roller  shafts,  forcing  the  feeding  rollers  apart  to  allow  entrance  of  the 
carbon. 

The  body  casting  of  the  negative  head  is  hinged  to  the  lever  arm  sho\vn  in 
figure  74,  and  is  held  in  the  running  position  by  a  latch  on  the  same  lever 
which  opens  the  rollers.  The  lever  arm  is  hinged  to  the  carbon  head  support 
and  is  held  in  the  starting  position  b}'  a  compression  spring.  When  the  carbons 
touch  after  the  main  lamj)  circuit  is  closed,  the  starting  rod  attached  to  the 
striking-magnet  armature  pulls  the  lever  arm  to  the  running  position.  The 
carbon-head  support  passes  over  a  foot,  which  is  insulated  from  the  top  plate 
of  the  lamp  casing,  and  is  held  in  position  by  nuts  on  four  studs.  These  nuts 
are  raised  or  lowered  on  the  studs  to  adjust  the  heads  to  the  proper  position 
in  the  barrel.  An  opening  is  provided  in  the  foot  which  communicates  with 
the  air  inlet  inside  of  top  plate  of  lamp  casing.  One  handle  for  Ufting  is  pro- 
vided on  each  end  of  the  lamp  and  winged  screws,  passing  through  holes  in 
the  clamps,  secure  the  lamp  in  the  lamp  trough. 

The  lamp  frame  is  composed  of  the  top,  bottom,  and  end  plates  and  sliding 
side  plates.  The  frame  incloses  the  negative  feeding  clutch,  striking  magnet, 
positive  feeding  magnet,  and  connection  plugs.  The  negative  feeding  clutch, 
figures  77  and  78,  operates  the  negative  feeding  rod. 


FIG.   72. -PARTS    OF    POSITIVE    ROTATING    MECHANISM.     G.    E.   24"    H.    P.    SEARCHLIGHT. 


-^^ 


v^o^ 


ft 


db 


FIG.   73. -PARTS    OF    CASING    FOR    POSITIVE    HEAD.     G.    E.  24"   H.    P.   SEARCHLIGHT. 


FIG.   74. -CARBON     HEAD    SUPPORTS    AND    FEEDING    RODS.     G.    E.   24"    H.    P.    SEARCHLIGHT. 


FIG.  75,     TOP    PLATE    WITH    GEARING.     G.   E.  24"   H.   P.   SEARCHLIGHT. 


FIG.    76.— PARTS    OF    TOP    PLATE    AND    GEARING.     G.    E.   24"    H.    P.    SEARCHLIGHT. 


FIG.    77.      NEGATIVE    FEEDING    CLUTCH.     G.    E.   24"    H,    P.    SEARCHLIGHT 


FIG.   78.— NEGATIVE    FEEDING    CLUTCH.     G.    E.   24"    H.    P.   SEARCHLIGHT. 


THE  SEABCHUGHT.  79 

(1)  In  the  "A"  or  automatic  position  of  the  negative  control  lever  on  the  rear 
end  of  the  lamp  the  negative  carbon  is  fed  forward  or  back  b}-  a  rotating  rod 
geared  to  the  feed  rollers.  At  the  lower  end  of  tliis  feed  rod  is  the  negative 
feed  clutch,  with  magnets  energized  by  the  relay.  When  the  relay  contact 
floats  and  neither  clutch  coil  is  energized,  the  feed  rod  is  stationary.  It  is 
rotated  to  feed  the  carbon  ahead  by  energizing  one  of  the  clutch  coils,  and  to 
feed  the  carbon  back  bj^  energizing  the  other  clutch  coil. 

(2)  In  any  of  the  hand-feed  positions  of  the  negative  control  lever  the 
carbon  is  moved  forward  by  means  of  worm  and  gear  driven  by  the  main  driv- 
ing shaft  of  the  lamp,  operated  by  the  handle  on  gear  casing  on  motor  compart- 
ment. When  in  the  hand-feed  position,  the  cam  on  the  contact  shaft  opens 
the  switch  in  the  clutch-coil  circuit. 

The  striking  magnet  armature,  figure  80,  operates  the  negative  lever  arm 
through  a  lever  and  rod.  The  full  cm-rent  taken  by  the  arc  passes  through 
the  coil.  A  relay  is  mounted  on  one  pole  of  the  magnet,  and  the  contact  arm 
is  held  in  a  mid-position  between  two  contact  points  when  the  current  of  the 
arc  is  of  the  proper  value. 

The  positive  feeding  magnet  armature,  figure  S2,  operates  the  positive 
feeding  rod,  which  engages  with  the  star  wheel  on  the  rotating  mechanism  of 
the  positive  head.  The  coil  is  connected  to  the  main  lamp  circuit  through  the 
thermostat. 

The  connection  plugs  are  mounted  on  the  end  plate,  as  shown  in  figure  84. 

OPERATION. 

PLACING    CARBONS    IN    LAMP. 

Release  rollers  in  positive  carbon  head  by  pressing  down  the  handle  at 
rear  of  head  untU  it  catches,  and  insert  positive  carbon  through  the  carbon 
tube  in  the  front  door,  pushing  it  through  the  head  until  it  projects  i  inch 
past  the  extreme  end  of  the  nose.     Push  up  handle  so  that  rollers  close. 

Release  rollers  in  negative  head  by  raising  the  handle  at  rear  on  negative 
carbon  head  to  the  extreme  position  which  allows  the  head  to  swing  into  a 
position  which  \vill  allow  the  carbon  to  pass  the  obdurator  on  the  positive  head. 
Insert  the  negative  carbon  through  the  negative  nose  letting  the  pointed  end 
project  i  inch  past  the  end  of  the  nose.  Push  the  head  back  to  running  position 
and  turn  handle  down  to  close  rollers. 

STARTING. 

(a)  Turn  handle  of  switch  in  base  to  the  "on"  position.  This  lights  the 
altitude  and  azimuth  scale  lamps  and  the  rccarboning  lamp  in  barrel,  and 
starts  the  ventilating  motor. 

(b)  Turn  handle  of  switch  on  barrel  to  the  "on"  position.  This  closes  the 
circuit  through  the  carbons  and  the  striking  magnet  coils,  thereby  establishing 
the  arc.  The  positive  feeding  magnet  and  negative  feeding  clutch  are  now  in 
circuit.  Switch  lever  on  thermostat  box  should  be  placed  at  "  on  "  position, 
putting  the  thermostat  in  circuit. 


80  THE   6EABCHLI0HT. 

RUNNING. 

The  end  of  the  positive  carbon  shoiild  show  on  the  line  on  the  arc  image 
screen.  The  control  levers  on  the  end  plate  should  be  placed  at  the  position 
marked  "A." 

STOPPING. 

Turn  handle  of  switch  on  baiTcl  to  the  "off"  position,  which  breaks  the  cir- 
cuit through  the  carbons,  but  allows  the  ventilating  motor  to  run. 

Turn  handle  of  switch  in  base  to  the  "off"  position,  which  stops  the  venti- 
lating motor  and  shuts  off  the  scale  lamps  and  the  recarbouing  lamp  in  baiTel. 


FIG.   79— PARTS    OF    NEGATIVE    FEEDING    CLUTCH.      G,    E.    24"    H.    P.    SEARCHLIGHT 


FIG.   80.— STRIKING     MAGNET     FOR    G.    E.   24"    H.    P.    SEARCHLIGHT. 


I 
o 

_l 
I 
o 
cr 
< 


FIG.   82. -POSITIVE    FEEDING    MAGNET.     G.    E.    24"    H.    P.    SEARCH- 
LIGHT. 


FIG.  83.— PARTS  OF  POSITIVE  FEEDING  MAGNET.     G.  E.  24"  H.  P.  SEARCH- 
LIGHT. 


dBn--^ 

■M    m     ^9      £      !^^^^^ 

t^ 

^^^-^T'M 

J^JMj 

Br 

9H 

<     w 

^^^^W"^*''*^^ 

k^^R^ 

FIG.  84.— CONTROL  END    PLATE    AND    CONNECTION     PLUG.     G.    E.  24"   H.    P.  SEARCHLIGHT.        t_J 


FIG.  85.— G.    E.  24-INCH    HIGH    POWER    SEARCHLIGHT.      PARTS    OF    CONNECTION    PLUGS. 


FIG.   86.— PARTS    OF    FRAME.      G.    E.   24"    H.    P.    SEARCHLIGHT. 


CHAPTER  6. 
ARMA  24-INCH  HIGH-POWER  SEARCHLIGHT. 


There  has  very  recently  been  developed  by  the  Arma  Engineering  Co. 
a  new  type  of  high-power  searchlight  for  naval  use.  This  lamp  was  de- 
veloped particularly  for  converting  present  30-mch  low-power  searclilights 
to  high-power,  and  also  for  making  a  complete  24-inch  high-power  searchlight 
with  a  drum  mounted  on  a  base. 

Past  experience  was  used  to  advantage  in  designing  this  light  and  it  has 
been  constructed  to  meet  the  severe  conditions  of  gunfire  shock,  spra}',  and  rough 
handling  to  which  Navy  searchlights  are  subjected.  Simplicity  has  been  empha- 
sized in  the  design  so  that  an  operator  may  disregard  the  operation  of  his  lamp 
and  concern  himseK  solely  with  keeping  it  trained  on  the  target.  The  great 
difference  between  this  searchlight  and  other  high-power  searchlights  is  in  the 
method  of  keeping  the  positive  carbon  in  focus.  This  is  done  by  means  of  a 
third  electrode  and  uses  the  arc  flame  as  a  conductor,  thus  doing  away  with 
thermostats,  mirrors,  prisms,  etc. 

Following  is  a  general  description  of  this  searchlight: 


POS.  r-£EO  A/t/7<?. 


£XMHUS  TMBTO/f 


nx  3C0H..C 


Fig.  87a.— Arma  21-incli.hIgh-po  ver.searehlight.    Wiring  diagram. 
6643S— IS 6 


81 


82 


THE   SEAECHLIUHT. 


^) 

^i£ 

1 

^? 

1 

^ 

5 

fc 

^ 

1 

! 

4 

FIG.   87.      ARMA    24"    HIGH     INTENSITY    SEARCHLIGHT.      END    VIEW. 


THE  SEAKCHLIGHT.  83 

LAMP  MECHANISM. 

A  J-horse-power  inclosed  shunt-wound  motor  connected  directly  across 
the  arc  supplies  the  drivmg  power  for  feeding  both  carbons  and  rotating  the 
positive.  A  centrifugal  governor  mounted  on  the  motor  shaft  operates  a 
reversible  three-disk  friction  clutch,  which,  tlirough  suitable  gearmg  and 
vertical  shaft  feeds  the  negative  carbon.  As  the  speed  of  the  motor  varies  with 
the  arc  voltage,  the  governor  causes  one  or  the  other  side  of  the  center  disk 
of  the  clutch  to  engage  its  adjacent  disk,  feeding  the  negative  carbon  in  the 
proper  direction  until  normal  arc  voltage  (and  consequently  normal  speed  of  the 
motor)  is  restored.  The  central  disk  of  the  clutch  then  revolves  freely  without 
engagmg  either  adjacent  disk,  so  that  the  negative  carbon  remains  stationary. 
The  same  clutch  mechanism  serves  to  strike  the  arc  by  rapidly  feeding  the 
negative  carbon  into  contact  with  the  positive  and  slowly  drawuig  it  back. 
While  constant  voltage  across  the  arc  is  maintained  by  this  arrangement 
within  very  close  limits,  it  may  be  desirable  to  alter  this  voltage  to  care  for 
variations  in  composition  of  carbons.  For  this  purpose  a  small  adjustable 
rheostat  is  connected  in  the  motor  field  and  is  mounted  in  a  convenient  loca- 
tion on  the  side  of  the  drum.  The  negative  carbon  head  is  arranged  for 
easy  recarbonmg. 

The  positive  carbon  is  rotated  by  a  pair  of  reciprocating  fingers  arranged 
on  opposite  sides  of  the  carbon,  and  so  mounted  that  they  bear  on  the  carbon 
for  only  half  of  their  complete  strokes.  The  carbon  is  consequently  rotated, 
step  by  step.  While  the  fingers  normally  reciprocate  at  right  angles  to  the 
axis  of  the  carbon,  they  are  arranged  to  be  deflected  by  a  solenoid  which,  when 
energized,  causes  them  to  reciprocate  at  an  angle  to  their  former  du-ection, 
thereby  feeding  the  carbon  forward  a  small  amount  with  each  stroke.  The 
reciprocation  of  the  fingers  is  accomplished  by  two  eccentrics  which  are  con- 
tinuously rotated  by  a  vertical  drive  shaft  which,  in  turn,  is  driven  from  the 
motor  shaft  by  a  worm  and  gear.  The  solenoid  which  controls  the  feed  of  the 
positive  is  energized  through  contact  of  the  arc  flame  with  an  auxiliary  elec- 
trode. Both  solenoid  and  electrode  are  mounted  on  the  positive  carbon  head, 
the  consumption  of  the  positive  carbon  brings  the  flame  into  electrical  contact 
with  this  auxiliary  electrode,  energizing  the  solenoid  and  feeding  the  positive 
carbon  (and  of  course  the  flame)  forward  until  contact  with  auxiliary  electrode 
is  broken.  The  fingers  then  drop  back  to  their  normal  positions,  continuing 
to  rotate  the  carbon  but  not  feeding  it.  The  exceedingly  slow  consumption 
of  the  auxiliary  electrodi^is  taken  care  of  by  a  very  shnple  device  which  maintams 
this  electrode  in  a  fixed  position.  The  entu'e  arrangement  of  solenoid,  feed 
mechanism,  and  electrode  is  absolutely  automatic  and  requires  no  adjustment 
of  any  sort.  It  should  be  noted  that  the  driving  motor  and  the  positive  feed 
solenoid  are  the  only  pieces  of  electrical  apparatus  in  the  lamp. 

DRUM  AND  BASE. 

Since  these  searchlights  are  constructed  for  anti-aircraft  as  well  as  ordinary 
naval  service,  the  drum  is  arranged  to  elevate  100°  above  and  30°  below  the 
horizontal  train.  Necessary  cooling  of  the  drum  is  obtained  by  an  e.xhaust 
fan  located  on  top  of  the  searchlight.     The  motor  which  drives  this  fan  oper. 


84 


THE   SEARCHLIGHT. 


iiG.  is.— Arma  21-mclj  UiuU-powct  seurclilnjljl.    lligbi  side  view. 


FIG.    88.-  ARMA    HIGH     INTENSITY    SEARCHLIGHT.      1,    CONTROL    ELECTRODE   SOLENOID;    2. 
CONTROL    ELECTRODE.     3,    CLUTCH    M  ECH  AN  ISM  :   4,    FLYWHEEL   GOVERNOR. 


-12 


-14 


FIG.    89.— ARMA   24"    HIGH     INTENSITY    SEARCHLIGHT.      SIDE    VIEW. 


THE  SEABCHLIGHT.  85 

ates  normally  at  60  volts,  but  is  designed  to  operate  safely  at  120  volts.  Its 
characteristics  are  such  that  the  starting  current  is  not  excessive.  It  is  mounted 
on  top  of  the  drum,  and  is  suitabh^  inclosed  to  insure  it  against  damage  from 
moisture,  while  at  the  same  time  allowing  of  necessary  ventilation.  The  mirror 
is  held  in  its  supporting  frame  by  spring  clips,  and  is  so  mounted  as  to  provide 
for  expansion.  The  mirror  ring  is  readily  removable  from  the  drum  for  inspecting 
and  cleaning  the  glass.  The  front  end  ring  of  the  dnim  contains  the  iris  shutter, 
which,  however,  maj'^  be  removed  if  necessary.  Ahandwheel  is  located  on  the  side 
of  the  drum  for  its  operation.  The  mounting  for  the  front  door  fits  in  the  iris 
shutter  ring,  and  is  supported  in  place  with  springs  to  prevent  breakage  from 
gunfire.  Provision  is  made  in  the  front  door  for  replacing  positive  carbon. 
A  Venetian  blind  shutter  is  mounted  on  the  front  of  this  door,  and  is  operated 
by  a  handle  projecting  from  theside.  A  ground  glass  finder  is  located  on  the  side 
of  the  drum,  and  gives  an  upright  fuU-sizcd  image  of  the  arc.  The  intensity  of 
this  image  is  adjustable  to  suit  conditions  of  use.  Peep  sights  on  either  side 
of  the  drum  afford  a  clear  view  of  the  arc  and  carbon  holders.  The  arc  length 
regulating  rheostat  is  located  adjacent  to  the  ground  glass  finder,  but  is  inside 
the  drum,  with  handle  projecting  outside.  A  scale  and  an  illuminated  pointer 
are  placed  on  the  trunnion  arm  for  indicating  vertical  train.  A  clamp  is  also 
provided  for  locking  the  drum  in  any  position.  Handles  projecting  from  the 
rear  of  the  searchlight  are  used  for  directing  the  beam,  while  a  sighting  arrange- 
ment on  the  side  of  the  drum  helps  in  following  a  rapidlj'  moving  target. 
Sliding  contacts  are  provided  in  the  lower  part  of  drum,  so  that  lamp  mecha- 
nism may  be  easily  installed  and  removed.  A  screw  projecting  from  the  drum 
and  engaging  the  lamp  serves  to  focus  the  beam,  which  operation  does  not 
interfere  in  any  way  with  the  automatic  feeds  of  the  lamp. 

The  upper  or  revolving  part  of  the  base  is  supported  around  its  circum- 
ference by  ball  bearings,  the  construction  being  such  that  moisture  is  pre- 
vented from  entering  either  the  bearings  or  base.  Attached  to  the  inside  of 
the  upper  base  and  revolving  with  it  is  a  quick  break  double  pole  switch, 
operated  by  a  handle  from  the  outside.  This  part  of  the  base  also  carries  the 
brushes  which  conduct  current  from  the  stationary  collector  rings.  Armored 
cables  in  water-tight  bushings  conduct  the  current  from  the  main  switch  in 
the  base  to  the  drum.  The  upper  part  of  base  carries  an  illuminated  pointer 
indicating  train  of  searchUght  on  a  stationary  azimuth  scale.  As  on  the  eleva- 
tion gear,  a  clamp  is  provided  to  secure  the  base  in  any  desired  angle  of  train. 

POWER  CONSUIVIPTION. 

Seventy-five  amperes  at  120  volts  are  required  for  the  best  operation. 


86 


THE  SEAKCHLIGHT. 


POSITll/E  HE/<D 


CONTROL 
tLECT  ROO 


UZGATIVE  HEAD 


Fig.  S9.— Arrna  21-inch  higb-pov  er  scsrchlight.    Ntmcs  ol  parts. 


FIG.  90. -SPERRY-G.    E.    36INCH     HIGH     POWER    CONVERTED    SEARCHLIGHT.      RIGHT    SIDE 

VIEW.      NAMES    OF  [PARTS. 


CHAPTEE  7. 

SPERRY  fflGH-POT\T:R  SEARCHLIGHTS  CONVERTED  FROM  GENERAL 
ELECTRIC  LOW-POWER  SEARCHLIGHTS. 


The  new  high-power  searchlights  are  so  far  superior  to  the  older  low-power 
searchlights  that  it  is  desirable  to  have  as  many  low-power  searchlights  as 
possible  replaced  bj'  high-power  searchlights.  To  accomplish  this,  a  method 
was  devised  whereby  a  low-power  General  Electric  Co.  drum  could  be  used, 
and  by  removing  the  old  lamp  and  putting  in  new  Sperry  high-power  lamp  and 
certain  accessories,  it  could  be  made  high  power.  This  saves  much  time  and 
expense,  and  does  not  necessitate  the  scrapping  of  the  low-power  drums. 

The  conversion  is  a  matter  of  some  difficulty,  and  is  best  done  in  navy  yards. 

The  method  of  converting  36-inch  General  Electric  low-power  searchlights 
to  high  power  is  set  forth  in  some  detail  in  this  chapter,  which  is  a  reproduction 
of  the  instruction  book  on  conversions  (published  by  the  Sperry  GjToscope  Co 
for  the  Navy). 

DiEECTIONS   FOE   CoNVEETIXG    SC-InCH    GENERAL   ELECTRIC   SeAECHLIGHTT. 
DISASSEMBLY  OF  GENERAL   ELECTRIC  PARTS. 

Remove  front  door,  old  lamp,  and  also  mirror,  if  possible,  as  it  makes  the  drum  more  conven- 
iently accessible. 

Remove  main  cables  from  the  lamp  compartment,  but  not  from  the  base. 

Remove  bottom  of  lamp  compartment. 

Contact  shoes  and  all  electrical  contact  studs  ma\'  now  be  removed  from  the  lamp  compart- 
ment.    Also  remove  the  old  focusing  screw. 

Drive  ths  insulating  bushing  out  of  the  hole  for  the  old  hand-feed  handle,  as  this  is  the  place 
where  the  new  focusing  screw  goes. 

Remove  the  hood  and  top  plate  of  the  drum,  using  a  fhatp  cold  chisel  and  alight  hammer  to 
cut  the  heads  off  the  rivets  in  the  bottom  p'ate,  one  man  holding  a  bar  or  hea\-\-  hammer  against 
the  rivet  on  the  inside  of  drum  to  prevent  denting  plate.  The  brass  p'ate  of  which  the  drum  is 
made  bends  very  easily,  and  care  must  be  exercised  in  working  on  same  to  prevent  denting,  as  this 
would  make  it  almost  impossible  to  prcpsrly  fit  the  parts  and  wcu'd  make  the  job  appear  bad. 

In  attaching  the  metal  forms  be  sure  that  the  parts  are  shrpcd  so  as  to  conform  to  the  shape 
of  the  drum  before  making  the  holes.  If  they  do  not  fit,  bend  ihcm  into  the  proper  shape  or  drill 
the  holes  so  that  the  bolts  will  draw  them  into  the  prep  jr  position.  In  drilling  in  the  sides  of  the 
drum  use  a  hand  or  breast  drill,  and  if  holes  are  drilled  frcm  the  cutside  have  a  man  hold  a  piece  of 
wood  on  the  inade  of  the  drum  against  the  sheet  metal  at  the  point  where  it  is  being  drilled,  to 
prevent  denting. 

ASSEMBLY   OF  CONVERSIOX   PARTS   ON   GENERAL    ELECTRIC   DRUM. 

The  following  order  of  assembly  indicates  the  best  melhcd  and  sequence  of  converting  the 
General  Electric  drum  for  use  with  Sparry  apparatus: 

,  (1)  Ventilating  hood  (figs.  93  and  94). — Place  ventilating  hoed  (1,  fig.  93)  on  top  of  drum  so 
that  vertical  center  line  of  the  drum  coincides  with  that  of  the  hoed.  Note  that  the  ventilating 
motor  (3,  fig.  931  shoiUd  be  at  the  mirror  end  of  the  drum  and  that  the  hoed  should  fit  between  the 

87 


88  THE  SEARCHLIGHT. 

front  and  rear  siippnrtins  rings  (3,  fig.  90)  of  the  drum.  Spot  all  holes  to  be  drilled  in  the  drum 
from  th^se  in  the  hiod  addition  plat&s  (2,  fig.  93);  drill  w-ith  clearance  drill  and  fit  screws  and  nuts, 
havini;  all  nuts  on  the  inside.  Peon  all  screw  ends  to  prevent  the  nuts  from  coming  off.  .\ttach 
blower  hood  (5,  fig.  93)  to  ventilating  hood. 

(2)  Instrument  box  and  plate  assembled  (fig.s.  94  and  95). — Locate  instrument  box  plate  (4,  fig. 
95)  on  right  side  (looking  forward)  of  drum;  left-hand  edge  of  plate  to  he  flush  against  rear  support- 
ing ring  (3,  fig.  90)  and  bottom  edge  of  plate  to  be  3J  inches  from  the  horizontal  renter  line  of  the 
drum.  Keep  rectangular  opening  to  the  rear  of  drum.  Spot  holes  on  drum  from  three  outside 
rows  of  holes  on  plate  (omitting  side  to  front).  Drill  holes  through  drum  and  fit  plate  on  drum 
bv  means  of  screws  and  nuts  on  the  inside  of  drum.     Peen  ends  of  screws. 

Remove  ground-glass  finder  (6,  fig.  94)  from  instrument  box  (2,  fig.  94). 

(3)  Rigid  air  duct  (figs.  90  and  97). — Locate  air  duct  (2,  figs.  90  and  97)  without  extension  on 
inside  surface  of  right-hand  side  of  drum  so  that  curved  end  fits  flush  against  addition  plate  (2, 
fig.  93)  of  hood  and  lower  end  fits  inside  of  General  Electric  air  inlet.  Spot  ground-glass  finder 
opening  in  instrument  box  plate  (2,  fig.  95)  on  air  duct.  Remove  air  duct  and  cut  out  opening 
from  scribed  line  and  finish  with  file.  Replace  ground-glass  finder  (6,  fig.  94)  in  instrument  box 
and  fit  duct  as  before.  Replace  and  drill  holes  in  drum  side  from  holes  in  air-duct  flanges  and  fit 
screws  and  nuts  as  holes  are  drilled.  Note  that  screw  beads  are  to  be  on  the  outside  of  drum. 
Peen  ends  of  fastening  screws. 

It  is  now  necessary  to  remove  General  Electric  air  inlet  to  make  room  for  Sperry  side  door 
(4,  fig.  98),  and  then  fit  Sperry  inlet  (24,  fig.  90). 

(4)  Drum  side  door  (fig.  98). — Locate  one  door  guide  (1,  fig.  98)  inside  drum  up  against  front 
ring  (3,  fig.  90)  of  drum,  lower  edge  to  be  IJ  inches  from  bottom  edge  of  drum  side  (junction  of 
drum  side  and  lamp  box).  Spot  holes  (No.  28  drill)  from  tapped  holes  in  guide  and  drill  clearance 
holes  (No.  18  hole)  in  drum.     Fit  guide  to  drum. 

Locate  drum  doorstop  (3,  fig.  98)  horizontally  as  shown  in  figure  98  and  fit  to  drum.  Take 
off  stop  and  locate  other  guide,  using  stop  as  spacer  to  keep  guides  parallel  Fit  other  guide; 
replace  stop.  Dismount  handle  (7,  fig.  98)  from  door  and  slide  door  in  guides  from  top  and  bring 
it  flush  against  doorstop  (3,  fig.  98).  Scribe  line  on  drum  side,  using  top  edge  of  door  as  guide. 
Remove  door.  Saw  opening  for  door  from  ecrilied  line,  guides  (1  and  2,  fig.  98)  and  stop  (3,  fig. 
98).     Finish  opening  by  filing.     Remount  handle  on  door  and  replace  door  in  guides. 

Locate  light  lock  strip  (5,  fig.  98)  on  drum,  pushing  in  from  bottom  until  flush  with  strip 
(0,  fig.  98)  on  door.  Rivet  to  drum.  See  that  drum  door  works  freely.  Locate  and  assemble 
snap  catch  (11,  fig.  00)  to  top  end  of  door  from  hole  in  top  strip  when  door  is  in  the  extreme  open 
position. 

(6)  Drum  patch  (fig.  90).— Fit  dnim  patch  (2,  fig.  90)  to  drum. 

(6)  Left-hand  air  duct  (figs.  90  and  97). — Locate  left-hand  air  duct  (1,  fig.  96)  similarly  to  right 
hand  air  duct  (2,  fig.  9G),  placing  extension  so  as  to  fit  on  General  Electric  air  inlet.  Fasten  to 
drum  side  in  the  same  manner  as  other  duct. 

(7)  Thermostat  (fig.  98). — Mount  thermostat  mirror  (6,  fig.  98)  on  drum  and  centrally  in  hous- 
ing (4,  fig.  97)  provided  in  air  duct.  Note  that  adjusting  screw  must  be  on  the  side  nearest  the 
parabolic  mirror. 

(8)  Glass  strips  and  clamp  (fig.  99). — Fit  glass  front-door  strips  and  clamp  (2,  fig.  99). 

(9)  Carbon  tube  and  supports  (fig.  99). — Mount  three  brackets  (4,  fig.  99)  on  front-door  ring 
(3,  fig.  90).  Fasten  one  end  of  the  three  long  and  three  short  support  rods  (5  and  6,  fig.  99)  to 
brackets  (4,  fig.  99).  Set  carbon  tube  (7,  fig.  99),  and  fasten  it  in  place  by  moans  ol  the  other 
end  of  the  support  rods  as  shown  at  19,  figure  90.  With  the  carbon  tube  in  place,  as  shown  at 
18,  figure  90,  unscrew  diaphragm  of  iris  shutter  centralizing  cone  (3,  fig.  99)  until  clearance  is 
obtained  to  slip  six  spicing  rods  (8,  fig.  99)  through  holes  provided  for  them  in  diaphragm.  Screw 
other  end  of  spicing  rods  in  iris  shutter  ring. 

(10)  Focusing  screw  (fig.  100). — Insert  focusing  screw  (5,  fig.  100)  in  hole  in  back  end  of 
lamp  box  and  fit  in  plies  by  attaching  bracket  (5i,  fig.  100)  to  lamp  box. 

(11)  Rack  stops  ifij.  100).— Fast3n  rack  stops  (7,  fig.  100)  to  elevating  rack,  as  shown  at  17, 
figure  90.  , 

(12)  Air-duct  screens  (fig.  100).— Fit  air-duct  screens  (1  and  2,  fig.  100)  to  air  inlets  on  outside 
of  dnun  by  spotting  holes  from  flange  of  screen  on  inlet,  drilling  and  tapping  inlet,  and  inserting 
screws. 


FIG.     91.— SPERRY-G.     E.     35-INCH      HIGH      POWER     CONVERTED     SEARCHLIGHT.      FRONT     VIEW. 


FIG.  92.-SPERRY-G.  E.  36-INCH   HIGH   POWER  CONVERTED  SEARCHLIGHT.     THREE-QUARTER 

LEFT    SIDE    VIEW. 


FIG.    93.— SPERRY-G.     E.    36-INCH     HIGH     POWER    CONVERTED    SEARCHLIGHT.       CONVERSION 

PARTS. 


FIG.    94.— SPERRY-G.    E.    36-INCH     HIGH     POWER    CONVERTED    SEARCHLIGHT.       CONVERSION 

PARTS. 


f»^ 

^^^    ^mP          ysy:  \*' 

-1h  ^ 

3             '^' 

FIG.    95.-SPERRY-G.    E.    361NCH    HIGH    POWER    CONVERTED    SEARCHLIGHT.       CONVERSION 

PARTS. 


FIG.    96.— SPERRY-G.    E.    36-INCH     HIGH     POVk'ER    CONVERTED    SEARCHLIGHT.     CONVERSION 

PARTS. 


FIG.    97— SPERRY-G.     E.    36-INCH     HIGH     POWER    CONVERTED    SEARCHLIGHT.     CONVERSION 

PARTS. 


FIG.    98.— SPERRY-G.    E.    36-INCH     HIGH     POWER    CONVERTED     SEARCHLIGHT.      CONVERSION 

PARTS. 


FIG.    99.-SPF.RRY-G.     E.    36-INCH     HIGH     POWER    CONVERTED    SEARCHLIGHT,      CONVERSION 

PARTS. 


FIG.    lOO.-SPERRY-G.    E.    36-INCH     HIGH     POV^ER    CONVERTED    SEARCHLIGHT.      CONVERSION 

PARTS. 


FIG.    101.— SPERRY-G.    E.    36-INCH     HIGH     POWER    CONVERTED    SEARCHLIGHT.      CONVERSION 

PARTS. 


FIG.    102. -SPERRY-G.    E.    36-INCH    HIGH    POWER    CONVERTED    SEARCHLIGHT.     CONVERSION 

PARTS. 


FIG.    103.     SPERRY-G.    E.    36-INCH    HIGH    POWER    CONVERTED    SEARCHLIGHT.     CONVERE  ON 

PARTS. 


■r.^^-^^=f 

1 

• 

^  :' 

• 
* 

E 

■    •    ■■ 

FIG.    104.— SPERRY-G.    E.    36-INCH    HIGH    POWER   CONVERTED    SEARCHLIGHT.     CONVERSION 

PARTS. 


THE  SEAKCHLIGHT.  89 

(13)  Peep  sights  (fig.  100). — Screw  on  peep  sights  (10  and  11,  fig.  100)  taking  care  to  fit  asbestos 
packing  on  both  sides  of  glass. 

(14)  Pivot-hole  patches. — Fit  both  pivot  hole  patches.  Circular  patch  fits  on  left-hand  side 
of  drum. 

(15)  Electricians'  work. — After  the  mechanical  assembly  is  made,  the  electricians  may  fit  the 
conduit  and  ammeter  box,  the  fuse  block,  and  wire  the  unit  according  to  the  supplied  diagram 
number. 

(16)  Conduit  to  instTument  box  and  motor  {6gB.  lOland  102). — Five  leads  in  this  conduit — three 
to  instrument  box  and  two  to  blower  motor. 

The  conduit  is  fitted  as  follows:  Lay  off  two  holes  on  front  right-hand  side  of  lamp  box  as  shown 
in  blue  print.  The  conduit  running  to  instrument  box  (5,  fig.  90)  is  placed  on  side  of  drum  nearest 
front  ring.     Piece  1,  figure  101,  is  fitted  to  drum  as  follows: 

(1)  Unscrew  nipple  (A)  and  remove  washer  (B)  and  packing  ring. 

(2)  Insert  end  of  conduit  in  hole  of  lamp  box  (14,  fig.  90)  so  that  washer  and  packing  are  snug 
against  side  of  box. 

(3)  Replace  packing,  washer  (B),  and  nipple  (A). 

(4)  Tighten  nut  (C)  until  conduit  is  securely  fastened  in  place. 

Fit  pieces  of  conduit  (1  to  7,  inclusive,  fig.  101)  in  order  as  shown  in  figure  102,  inserting  snap 
switch  (9,  fig.  101)  between  conduits  (4,  5,  and  7)  and  inserting  end  of  conduit  (7)  in  instrument 
box  connection  housing  (10,  fig.  101).     Run  conduit  (6)  up  to  ventilating  hood  (1,  fig.  93). 

To  fasten  conduits  (1)  and  (8)  to  drum,  use  double  straps  (13,  fig.  100).  To  fasten  conduit 
(6,  fig.  101)  to  ventilator  hood  (1,  fig.  93)  use  single  strap  (12,  fig.  100).  Use  half  straps  (14,  fig.  100) 
to  fasten  other  conduit  to  drum. 

(17)  Conduit  to  ammeter  box  (fig.  101). — Four  leads  in  this  conduit — two  to  ammeter  box  and 
two  to  ammeter. 

Mount  end  of  conduit  (8,  fig.  101)  leading  to  lamp  box  (14,  fig.  90)  similarly  to  conduit  (1, 
fig.  101). 

(18)  Ammeter  box  (figs.  93  and  101). — To  fit  ammeter  box  (11,  fig.  101)  to  drum,  place  the  box 
on  the  tie  rods  (26,  fig.  90)  so  that  brackets  (IID  and  HE,  fig.  101)  hook  over  the  upper  and  lower 
tie  rods,  respectively.    Tighten  screw  (IIF,  fig.  101). 

(19)  Fuse  block  (figs.  93  and  100). — Mount  fuse  block  (4,  fig.  100)  on  top  of  ventilating  hood, 
fuses  to  run  crosswise. 

(20)  Bottom  plate  of  lamp  box  (figs.  103  and  104). — To  mount  bottom  plate  of  lamp  box  place 
in  position  with  condenser  (2,  fig.  103)  and  ammeter  shunt  (3,  fig.  103)  to  front  of  drum.  Spot 
holes  in  lamp  box  from  those  in  plate;  drill,  tap,  and  fit. 

(21)  \\'ire  and  fit  lamp. 

(22)  Adjust  counterbalance  weights  on  lamp  box  tie  rods. 


CHAPTER  8. 
LOW-POWER  SEARCHLIGHTS. 


Until  the  high-power  searcUight  was  developed,  the  standard  pure  carbon 
arc  searchlight  was  used  exclusively-  The  range  of  the  best  Navy  searchlight 
using  pure  carbon  arcs  is  about  6,000  yards  on  clear,  dark  nights,  at  which 
distance  a  target  may  be  made  out  with  the  iiso  of  binoculai-s.  Range  finder 
readings  could  not  bo  taken  at  distances  gi-eater  than  about  2,500  yards  when 
target  was  illuminated  by  one  36-inch  searchlight. 

'Die  advent  of  the  high-power  searchlight  with  a  beam  candlepower  of  about 
seven  times  that  of  the  pure  carbon  arc  searcUight  and  more  than  double  the 
range,  immediately  made  low-power  searchlights  obsolete. 

Low-power  searclilights  are  furnished  ships  of  the  Navy  in  the  following 
sizes:  36-,  30-,  24-,  18-,  12-,  and  9-inch.  All  searchlights  are  aiTanged  for  auto- 
matic feed  of  carbons,  two  tj-pes  of  feed  being  used,  the  ratchet  feed,  supplied 
b}'  the  General  Electric  Co.,  and  motor  feed,  supplied  by  the  Carlisle  &  Finch  Co. 

The  mechanism  of  the  low-power  searchlight  is  ver}'^  simple  as  compared 
with  the  mechanism  of  the  high-power  light,  no  forced  coohng  ])eing  provided, 
nor  is  any  provision  made  for  revolving  the  heads  through  which  the  carbons 
feed. 

Specifications  for  various  ti^jcs  of  lights  are  given,  followed  by  description 
of  a  typical  low-power  searchlight. 

The  12-inch  arc  signaling  searchlight  is  treated  xmder  chapter  4. 

Specifications  for  18-,  24-,  30-,    and  36-Inch   Low-powered  Searchlights   foe  Use  in 

THE  United  States  Navy. 

[JUNE  5,  1917.] 

1.  General  specifications  for  the  inspection  of  material  issued  by  the  Navy  Department, 
in  effect  at  date  of  openinj;  of  bid,  shall  form  part  of  these  specifications. 

2.  The  searchlights  will  be  designated  by  the  follo\ring  types  and  will  be  designed  to  be 
operated  on  a  lino  voltage  of  125  unless  otherwise  specified. 

(a)  Hand  control. 

(6)  Distant  electrical  control. 

(c)  Distant  mechanical  control,  type  A,  B,  C,  or  D. 

3.  General  for  aU  types. 

(d)  Drum. — The  drum  will  be  made  of  brass  and  hive  openings  which  permit  of  easy  access 
to  the  lamp  mechanism  and  mirror.  All  op3nings  in  the  drum  will  be  so  covered  as  to  exclude 
w-ind  and  rain  and  pDrmit  the  light  to  be  operated  without  flickering  when  the  wind  blow  s  at  the 
rate  of  30  statute  miles  per  hour.  The  covers  will  be  so  placed  on  the  drum  that  w  hen  the  shutter 
is  closed  and  th*?  light  is  burning  thore  will  be  no  light  visible  at  a  distance  of  10  meters  (about 
33  feet)  in  any  direction  from  the  searchlight.  A  calibrated  ground-glass  finder  will  be  fitted  in 
the  drum  in  a  convenient  position,  and  will  give  an  upright  full-sized  image  of  the  arc  on  the 
ground  glass.  It  will  also  show  the  image  of  each  carbon  and  be  marked  to  indicate  the  correct 
position  for  same,  so  that  the  arc  can  be  kept  in  correct  length  and  in  the  focal  point  of  the  mirror. 

90 


THE  SEARCHLIGHT.  91 

Provision  will  be  made  for  varying  the  intensity  of  the  image  on  the  groimd-glaes  finder  to  meet 
day  and  night  conditions  of  operation.  It  -nill  be  capable  of  permitting  operator  to  watch  the  arc 
without  any  light  being  visible  at  a  distance  of  200  meters  (about  656  feet)  from  the  searchlight. 
A  metal  hinge  cover  over  ground-glass  finder  ^vill  be  provided. 

Two  small  "arc  weld"  or  electric  smoked-glass  observing  openings  with  metal  covers  will 
be  placed  in  a  convenient  section  of  the  drum.  They  will  permit  a  clear  and  imblurred  view  of 
the  arc  and  make  visible  the  electrode  holders. 

The  drum  will  be  so  ventilated  that  during  a  continuous  run  of  one  set  of  carbons  the  tem- 
perature rise  will  not  endanger  the  mirror  or  any  other  part  of  the  searchlight. 

The  ventilation  shall  be  sufficient  to  prevent  the  deposit  of  enough  fumes  on  the  mirror  during 
10  hours'  usage  to  materially  impair  its  reflecting  power.  It  will  be  of  sufficient  capacity  to  carry 
off  heat  at  such  a  rate  that  with  the  shutter  closod  and  the  arc  biu-ning  under  normal  conditions 
th?  temparature  shall  not  endanger  the  mirror.  The  ventilating  system  will  not  cause  any  flicker- 
ing of  the  arc.  It  -will  be  possible  to  open  the  drum  doors  while  the  arc  is  biirning. 
The  drum  will  be  so  designed  that  the  lamp  mechanism  can  be  easily  removed. 
The  barrel  will  carry  a  spirit  level  suitably  mounted  to  enable  the  operator  to  keep  the  barrel 
level  whsn  operating  the  searchlight  by  hand. 

A  sighting  arrangement, consisting  of  two  suitable  gun  sights,  will  be  mounted  on  the  left-hand 
side  of  barrel  facing  mirror. 

Arrangements  will  be  made  for  the  adjustment  of  the  positive  carbon  in  both  the  vertical  and 
horizontal  planes,  also  for  rotating  the  positive  carbon,  by  means  of  handwheels  on  the  exterior 
of  the  barrel.  The  connections  betv.-een  handwheels  and  carbon  holder  will  be  such  as  to  permit 
ready  removal  of  the  lamp  from  the  barrel. 

(e)  Front  door  and  strips. — The  front  door  shall  consist  of  a  light  composition  ring  which  will 
be  readily  removable  from  the  drimi,  and  be  designed  to  hold  the  front  door  strips,  iris  shutter, 
and  Venetian  blind  shutter.  When  in  place  it  will  be  so  supported  by  springs  and  rollers  to 
eliminate  breakage  due  to  gunfire. 

The  front  door  strips  will  be  secm'ely  moimted  in  a  composition  ring  and  each  strip  will  be 
readily  removable  from  the  ring.  They  will  be  of  clear,  white,  plate  glass,  with  siu-faces  parallel 
and  highly  polished.  The  edges  of  strips  will  be  at  right  angles  to  the  surfaces  and  have  a  ground- 
glass  finish. 

Where  radial  strips  are  furnished  all  strips  will  be  identical  in  shape  and  reinforced  as  neces- 
sary to  withstand  the  shock  of  gunfire. 

The  composition  ring  holding  front-door  strips  will  be  securely  mounted  in  the  front  door  and 
be  easily  removable.  The  ring  will  be  so  supported  in  the  di-um  by  clamps  and  springs  as  to 
eliminate  breakage  due  to  gun  fire. 

(/)  Dome. — The  dome  shall  consist  of  a  composition  mirror  ring,  to  which  are  secured  a  sheet- 
copper  mirror  covering  and  two  lifting  handles.  The  dome  will  be  fastened  by  clamps  and  springs 
to  the  drum  in  a  manner  so  as  to  eliminate  bre.x!<age  due  to  gunfire.  These  clamps  to  be  so  designed 
as  to  enable  the  operator  to  readily  detach  the  dome. 

(g)  Trunnion  arms. — The  trunnion  arms  will  be  made  of  bronze,  pressed  or  cast  steel,  and  v.ill 
be  of  sufficient  height  to  permit  the  drum  to  be  elevated  at  least  45°  above  or  30°  below  the  hori- 
zontal Irain.  They  will  be  securely  fastened  to  the  rotating  section  of  the  base.  A  suitable  B:ale, 
graduated  in  degi'ees,  will  be  provided  to  indicate  the  amount  of  elevation  of  the  drum.  A  small 
covered  light  with  switch  will  he  placed  over  the  pointer  so  as  to  illuminate  the  pointer  and  scale 
immediately  under.  One  trunnion  arm  will  carr\-  a  suitable  clamp  for  seeming  searchlight  at  any 
degree  of  elevation  or  depression. 

(/()  Base. — The  base  will  consist  of  two  parts — a  stationary  lower  part  and  a  rotating  upper 
part.  The  base  will  be  hollow,  cii'cular  in  shajie,  and  made  of  ii'on  or  composition.  A  circular 
flat  gi-aduated  (degrees)  scale  will  be  securely  fastened  to  the  stationaiy  part  of  the  Iiase  and  an 
indicating  pointer  will  be  placed  on  the  rotating  section  to  indicate  the  angle  of  train  of  the  search- 
light. A  small  covered  light  with  switch  will  i;e  placed  over  the  pointer  so  as  to  illuminate  the 
pointer  and  scale  immediately  under.  The  base  will  contain  a  clamp  arrangement  for  holding  the 
drum  in  any  fixed  angle  of  train. 

The  base  will  contain  a  connection  board  for  convenient  connection  to  the  exterior  circuits. 
Plunger  contacts  to  be  provided  for  conductmg  the  current  to  the  lamp  by  means  of  slip-rings 
on  the  turntable.     Suitable  handholes,  permitting  access  to  the  connections,  shall  I,e  provided 


92 


THE  SEABCHLIGHT. 


and  shall  be  protected  by  a  aheot-motal  cover  drawn  tightly  into  poeition.  The  base  shall  be  con- 
structed so  as  to  permit  l)eing  securely  bolted  to  the  deck. 

((')  Mirror  and  mirror  holder. — The  mirror  will  be  in  strict  accordance  with  specification 
17M:ia,  copies  of  whi''h  can  be  obtained  upon  application  to  the  Bureau  of  Steam  Enijiiiecring. 
The  mirror  will  be  mounted  in  the  composition  mirrorin;;.  An  asbestos  material  approximately 
*  centimeter  (0.19GS5  inr-h)  thick  and  2.5  centimeters  (0.98125  inch)  wide  will  be  placed  between 
the  mirror  rin?  and  mirror  to  insure  a  snug  fit.  A  space  of  \  centimeter  (O.lOGS.j  inch)  between 
the  edge  of  mirror  and  mirror  ring,  to  allow  for  any  e.xpansion  of  the  mirror  duo  to  heat,  will  Vie 
fdled  in  with  asbestos  material. 

(j)  Lamp  raechanism. — The  lamp  will  be  of  the  double  feed  carbon  type,  constructed  so  that 
the  operator  has  eisy  access  to  all  working  parts.  The  lamp  will  be  designed  for  1  to  1  ratio  carbons, 
both  automatic  and  hand  feed  for  carbons,  and  the  change  in  feed  will  be  easily  accomplished 
while  lamp  is  in  operation.  The  lamp  will  have  hand  device  for  rotating  the  positive  carbon. 
The  feeding  arrangement  will  be  sn  designed  as  to  maintain  an  arc  voltage  between  values  specified 
in  the  talile  below.  The  lamp  and  drum  will  be  so  designed  that  new  carjions  may  be  put  in  and 
light  started  up  within  a  period  of  eight  minutes  from  the  time  the  light  is  turned  oCf.  The  lamp 
will  be  designed  for  current  as  specified  in  the  following  table: 


Size  of 
.iparcli- 
liRlit. 

Current 
am|)cres. 

Arc 
voltage. 

n 

24 
30 
30 

35 
SO 
SO 
120 

50-54 
SO-.M 
5,>-.i9 
SS-02 

The  positive-carbon  holder  will  be  mounted  in  a  horizontal  position  and  the  negative-carbon 
holder  may  also  be  horizontal,  orplaf~e:lat  an  angle  with  the  horizontal  center  line  of  the  positive- 
carbon  hoUFer  so  as  to  give  the  best  burning  condition  of  the  carbon  and  maximum  intensity  of 
light  flux  on  miri-or. 

The  lamp  will  be  as  light  and  compact  as  practicable,  consistent  with  strength. 

The  connections  inside  the  lamp  mechanism  will  be  firmly  secured  in  place,  and  the  entire 
lamp  mechanism  will  withstand  a  dielectric  test  of  1,500  volts  A.  C.  applied  for  one  minute. 

(k)  Shullcrs. — .MI  shutters  will  be  made  of  light  non-corrosive  material.  A  suitable  hand- 
wheel  for  operating  the  iris  shutter  through  gears  will  be  located  on  the  side  of  the  frum,  where  it 
is  easily  accessible  for  the  operator.  The  Venetian  blind  shutter  will  be  operated  by  a  handle 
located  on  the  side.  All  searchlights  will  be  supplied  with  iris  shutters  and  Venetian  blind 
shutters. 

(l)  Rheoslal. — The  rheostat  will  be  of  the  unit  typo,  and  must  be  sufficiently  inclosed  for  pro- 
tection against  injury,  and  at  the  same  time  allow  effective  ventilation.  A  suitable  insulated 
board  containing  resistance  contacts  and  rheostat  handle  will  be  mounted  on  the  rheostat.  The 
rheostat  will  consist  of  two  sections,  a  variable  and  fixed  resistance.  The  variable  resistance  will 
be  divided  into  at  least  10  steps,  each  step  giving  when  hot  approximately  a  drop  of  1  volt  when 
the  normal  current  of  the  searchlight  flows  through  them.  The  elements  will  be  thoroughly 
protected  against  corrosion  in  such  a  manner  as  not  to  give  off  objectionable  smoke,  and  securely 
fastened  in  the  supporting  frame  at  a  sufficient  number  of  points  to  prevent  damage  from  shocks, 
and  the  method  of  mounting  will  permit  a  ready  connection  of  the  leads  and  removal  of  grids  for 
repairs.  A  pan  will  be  installed  underneath  to  catch  any  molten  metal  or  displaced  pieces, 
should  the  elements  become  melted  or  broken  at  any  point.  The  total  resistance  from  cold  to  hot 
shall  not  exceed  12  per  cent  of  cold  resistance.  Connections  between  rear  panel  and  resistance 
unit  will  be  made  with  commercial  fireproof  wire.  The  temperature  rise  on  frame  will  not  exceed 
125°  C.  The  rheostat  will  withstand  an  overload  of  50  per  cent  in  amperes  for  a  period  of  10  min- 
utes continuously  without  damage. 

(m)  Carbons. — The  carbons  will  be  of  the  1  to  1  ratio  type,  and  in  strict  accordance  with 
Specifications  17C5,  latest  issue,  copies  of  which  may  be  obtained  upon  application  to  the  Bureau 
of  Steam  Engineering. 


THE   SEARCHLIGHT.  93 

4.  Types  of  control. 

(n)  Distant  mechanical,  type  A. — The  controller  will  consist  of  two  separate  composition  gear 
boxes,  in  accordance  with  Bureau  of  Steam  Enginoeting  plan  19S2S32L.  Copies  of  this  plan 
can  bo  obtained  upon  application  to  the  Bureau  of  Steam  Engineering,  Navy  Department, 
Washington,  D.  C. 

(o)  Distant  mechanical,  type  B. — The  controller  will  consist  of  one  composition  gear  box  and 
handwheels,  mounted  on  composition  pedestal,  and  connected  by  concentrated  pipe  shafts  to 
searchlight.  The  searchlight  will  be  controlled  by  three  handwheels  mounted  on  gear  box,  and 
connected  to  shafts.  Two  handwheels  on  opposite  sides  of  box  will  control  the  angle  of  train, 
and  the  third  handwheel  will  control  the  angle  of  elevation  and  depression.  Illuminated  dials 
will  be  installed  in  gear  box  to  indicate  the  number  of  degrees  elevation  or  depression,  and  also 
the  angle  of  train.  Means  will  be  provided  for  disengaging  the  mechanical  control  and  operating 
the  searchlight  by  handwheels  located  thereon. 

(p)  Distant  mechanical,  typo  C. — The  controller  will  consist  of  gear  box,  handwheels  for  con- 
trol, illuminated  dials,  and  means  for  disengaging  from  searchlight,  as  spocilied  under  (o),  but 
designed  to  mount  in  a  single  searchlight  trestlcwork  tower,  with  handwheels  mounted  outside 
of  tower  sides,  and  connected  to  gear  box  by  shafting. 

(q)  Distant  mechanical,  type  D. — The  controller  will  consist  of  gear  box,  illuminated  dials, 
and  moans  for  disengaging  from  searchlight  as  specified  under  (o),  but  designed  to  mount  in  a 
double  searchlight  trestlework  tower  with  two  handwheels,  one  for  control  of  elevation  and  de- 
pression, and  one  for  control  of  angle  of  train,  mounted  outside  of  tower  sides  and  connected  to 
gear  box  by  shafting. 

(r)  Distant  electrical. — The  distant  electrical  controller  ^rill  consist  of  two  separate  composition 
boxes,  mounted  on  composition  pedestals;  the  design  of  the  electrical  controller  will  be  such  as 
to  move  the  searchlight  without  jerk.  The  controller  will  be  capable  of  training  the  searchlight 
at  a  minimum  speed  of  3°  per  minute,  and  a  maximum  speed  of  3G0°  per  minute.  It  will  also 
be  capable  of  elevating  or  depressing  the  searchlight  at  minimum  speed  of  3°  per  minute,  and  a 
maximum  speed  of  180°  per  minute.  One  controller  will  control  elevation  and  depression,  and 
one  vnW  control  the  angle  of  train.  The  controller  will  be  as  light  in  weight  as  possible  without 
sacrificing  strength  and  satisfactory  operation.  Means  mil  be  provided  for  disengaging  the 
electrical  control  and  operating  searchlight  by  hand. 

5.  Material. — All  working  parts,  interior  bolts,  nuts,  pins,  screws,  springs,  brush  holders, 
and  studs  will  be  noncorrodible  material  thoroughly  shearadized,  heavily  copper  plated,  or  other- 
wise thoroughly  coated  to  prevent  corrosion, 

6.  Insulation. — All  insulation  shall  be  of  approved  insulating  material.  Hard  rubber  and 
porcelain  are  not  approved. 

7.  Motors  and  auxiliaries. — All  motors  and  auxiliaries  will  be  in  strict  accordance  with 
specifications  17A3,  latest  issue. 

8.  Wire. — All  wire  except  fireproof  and  magnet  wire  will  bo  in  strict  accordance  with  speci- 
fications 15C1,  latest  issue,  and  magnet  wire  will  be  in  strict  accordance  with  specifications  15W2b 
unless  otherwise  specified. 

9.  Finish.     All  exterior  surfaces  of  searchlight  will  be  finished  in  battleship  gray. 

10.  Instructions. — Contractor  will  furnish  with  each  searchlight  a  pamphlet  containing 
instructions  lor  operation  and  care  of  searchlight. 

14.  Drawings. — The  vertical  dimension  of  tracings  in  all  cases  will  be  27  inches. 

Specifications  foe  12-inch  Hand-Control  Arc  Searchlights  fob  Submarines. 

[APRIL  11,  1917.] 

1.  General  specifications  for  the  inspection  of  material  issued  by  the  Navy  Department, 
in  effect  at  date  of  opening  of  bids,  shall  form  part  of  those  specifications. 

2.  General. — The  material  shall  be  of  the  best  quality  and  workmanship  and  consist  of  a 
12-inch  searchlight,  fitted  for  use  on  a  submarine  boat.  The  searchlight  shall  be  designed  with 
a  special  reference  to  quick  striking  below  decks  through  hatches  27  inches  in  diameter. 

The  projector  shall  consist  of  a  brass  drum,  Mangin  mirror,  lamp,  rheostat,  two  sockets,  front 
door  with  glass  strips,  signal  shutter  with  operating  levers,  connecting  cable,  and  tool  box. 

Each  searchlight  shall  be  supplied,  among  others,  with  spare  parts  as  follows:  Twenty-five 
pairs  of  carbons  In  tin  box,  all  to  be  in  accordance  with  latest  specifications  issued  by  the  Navy 
Department. 


94  THE  SEARCHLIGHT. 

A  diapram  of  actual  connectionB  shall  be  pasted  or  otherwise  securely  attached  inside  the 
cover  of  the  tool  box.  This  diagram  shall  be  shellacked  or  otherwise  suitably  protected  against 
the  weather. 

3.  DnuQ. — The  drum  shall  bo  made  of  low  sheet  brass  at  least  No.  18  Brown  &  Sharpe  gauge, 
and  shall  be  supported  on  trunnions  in  a  manner  to  permit  a  movement  in  the  vertical  plane  of 
90°  above  and  90°  below  the  horizontal,  the  latter  angle  to  permit  the  barrel  being  placed  in  a 
safe  and  secure  position  for  lowering  below. 

The  drum  shall  have  ample  ventilating  facilities.  It  shall  be  fitted  with  cast  braes  and  rings 
and  copper  mirror  shield. 

Handles  shall  be  provided  at  the  rear  of  the  dnun  for  training  the  beam  and  a  clamp  shall  be 
provided  for  clamping  the  8»archlight  drum  in  any  position  between  limits  specified  above. 

4.  Anns  and  base. — The  trunnion  arms  and  sub-base  may  be  cast  in  one  piece  and  cast 
steel  is  permitted.  The  sub-base  shall  be  water-tight  and  contain  a  25-ampere  double-pole  snap 
switch  and  non-turning  binding  posts  for  connections. 

5.  Connections. — Two  cables  connecting  the  lamp  and  sub-baee  shall  be  brought  into  drum 
in  weatherproof  manner  and  into  trunnion  base  through  water-tight  stuffing  boxes.  A  flexible 
type  National  Electrical  Code  cable  may  be  used.  Stuffing  boxes  shall  be  of  J-inch  size.  An 
18,000  cm.  plain  twin  conductor  cable,  conforming  to  specifications  lof'lb,  shall  be  led  into 
sub-base  through  an  anti-kink  spring,  terminal  tube,  and  securing  clamp  in  a  manner  such  that 
sub-base  will  be  water-tight  and  searchlight  may  be  lowered  by  the  cable.  It  will  be  25  feet  long 
and  coupling  or  plug  need  not  be  supplied. 

6.  Socket. — A  cast-brass  railing  socket  capable  of  clamping  on  niiling  stanchion  of  from 
11  to  2i  inches  diameter  shall  support  the  entire  searchlight.    Two  sockets  shall  be  supplied. 

7.  Mirror. — The  mirror  shall  be  of  the  Mangin  type,  accurately  ground  and  polished  and 
silvered  in  a  durable  manner  to  withstand  the  heat  of  the  arc.  Silvering  shall  be  protected  by 
one  heavy  coat  of  metallic  copper,  and  on  this  copper  plating  a  coating  of  heavy  enamel  shall  be 
applied  which  shall  so  seal  the  backing  as  to  render  it  absolutely  waterproof  and  air-tight. 

The  mirror  shall  be  flexibly  mounted  in  its  supporting  ring  to  allow  the  expansion  and  con- 
traction due  to  heating  and  cooling.  The  mirror  shall  conform  to  all  requirements  of  Specifications 
17M7,  dated  1918.  Mirrors  shall  be  of  the  12-Lach  size,  but  the  mirror  frame  shall  be  capable  of 
adjustment,  so  that  dimension  "B"  may  be  -^  to  3J  inches  outside  diameter. 

8.  Front  door. — The  front  door  shall  contain  glass  strips  conforming  to  Specifications  17S1, 
issued  by  the  Navy  Department. 

9.  SigTial  shutters. — The  signal  shutter  shall  be  of  the  Venetian  blind  type,  in  accordance 
with  Bureau  of  Steam  Engineering  drawing  19-S-2769-L,  easily  operated  with  one  liand  and  held 
normally  closed  by  a  spring,  but  capable  of  being  locked  open. 

Handle  shall  bo  mounted  on  right-hand  side  facing  rear  of  searchlight. 

It  shall  be  so  mounted  on  the  front  of  searchlight  as  to  prevent  possibility  of  leakage  of  light. 

The  leaves  of  the  shutter  shall  be  as  light  as  possible  consistent  with  strength. 

All  parts  shall  be  made  of  noncorrodible  material. 

The  signal  shutter  shall  be  easily  removable  from  and  replaced  on  the  front  of  searchlight. 

10.  Lamp.— The  lamp  shall  be  of  the  horizontal  carbon  type,  with  the  carbons  in  the  axis 
of  the  mirror  and  be  designed  for  operation  at  approximately  20  amperes.  Provision  shall  be 
made  for  the  adjustment  of  the  positive  carbon  in  two  planes. 

The  feeding  magnets  shall  be  so  designed  that  the  searchlight  may  be  operated  continuously 
for  two  hours,  on  any  line  voltage  from  100  to  160  volts,  without  automatic  cut-outs. 

Magnet  coils  shall  withstand  160  volts  for  two  hours  without  injurious  heating,  with  arc  circuits 
uninterrupted. 

The  positive  and  negative  carbons  when  burned  under  normal  operating  conditions  shall 
bum  at  a  suitable  ratio. 

The  lamp  shall  operate  satisfactorily  on  the  arc  potential  of  45  volts  after  the  arc  is  satisfactorDy 
established. 

The  carbon  feeding  mechanism  shall  be  of  approved  positive  screw-feed  tj-pe  for  feeding  the 
carbons  together  at  the  proper  rates.  Arrangement  for  striking  the  arc  automatically  shall  be 
provided,  \\1ien  the  carbons  are  burned  out,  the  feeding  circuit  shall  be  opened  by  a  limit  snitch 
actuated  by  lamp  carriage.     Carbons  will  conform  to  advance  sheet  No.  51  of  March  8,  1917. 

11.  Rheostats.— The  rheostat  shall  be  suiuble  for  use  on  circuits  ranging  from  100  to  160 
volts. 


THE   SEARCHLIGHT.  95 

The  rheostat  shall  be  sufficiently  inclosed  for  protection  against  injury  and  at  the  same  time 
allow  effective  ventilation. 

The  elements  shall  be  so  supported  that  they  will  not  become  displaced  nor  fall  out  in  case 
they  should  be  melted  or  broken  at  any  point  and  should  be  so  constructed  that  each  ssction  may 
be  readily  replaced. 

A  suitable  insulated  board  containing  resistance  contacts  and  rheostat  handle  shall  be  mounted 
on  the  rheostat. 

All  contacts  shall  be  arranged  so  as  to  prevent  sparking. 

The  rheostat  shall  consist  of  two  sections,  a  variable  and  a  fixed  resistance. 

The  elements  shall  be  of  noncorrosive  material  and  the  resistance  increase  from  cold  to  hot 
shall  not  exceed  8  per  cent.  Connections  between  rear  of  panel  and  resistance  unit  shall  be  made 
with  commercial  fireproof  wire.  The  temperature  rise  on  any  part  of  frame  shall  not  exceed 
125°  C. 

12.  Finish. — The  entire  searchlight  shall  be  finished  in  slate  gray. 

13.  Name  plates. — A  name  plate  showing  manufacturer's  name  or  monogram  shall  be  fitted 
to  the  searchlight  in  a  conspicuous  place. 

14.  Material. — With  the  exception  of  parts  otherwise  specified  above  all  parts  shall  be  made 
of  non-corrosive  material.     Magnetic  parts  shall  be  suitably  protected  against  corrosion. 

15.  Tool  box. — With  each  searchlight  a  tool  box  shall  be  supplied  containing,  among  others, 
parts  as  follows: 

1  spare  set  glass  front-door  strips. 

1  spare  set  of  springs  for  all  lamp  magnets. 

1  spare  set  carbon  clamps. 

1  spare  set  insulation  for  lamps. 

1  spare  contact  screw. 

1  spare  shutter  spring. 

1  chamois  skin. 

1  dust  brush. 

1  carbon  clamp  wrench. 

1  small  wrench  for  8/32-10/32  nuts. 

16.  Instructions. — ^The  contractor  shall  furnish  with  each  searchlight  a  pamphlet  containing 
instructions  for  operation  and  care  of  searchlight  together  with  blue  prints  showing  diagrams  of 
elementary  and  actual  connections.  These  shall  be  supplied  in  tool  box  mentioned  above  lq 
paragraph  15. 

17.  Insulation. — All  insulation  shall  be  of  approved  insulating  material.  Porcelain  is  not 
an  approved  material  for  use  on  searchlights  or  rheostats. 

18.  Approval  of  type. — Searchlights  supplied  under  this  specification  shall  be  of  a  type 
which  has  been  approved  prior  to  time  set  for  the  opening  of  bids. 

In  the  event  that  type  proposed  to  be  furnished  has  not  been  approved  by  the  Bureau  of 
Steam  Engineering,  sample  of  complete  searchlight  shall  be  forwarded  to  the  navy  yard,  New 
York,  for  test. 

The  specifications  for  9-inch  hand-control  searchlights  for  submarines  are 
almost  the  same  as  those  for  the  12-inch  light  for  submarines.  Below  are 
given  the  points  of  difl'erences  between  the  two. 

Specifications  for  9-Inch  Hand  Control  Searchlights  for  Submarines. 

[february  2, 1916.] 
general. 

The  material  shall  be  of  the  best  quality  and  workmanship  and  consist  of  a  9-inch  searchlight, 
fitted  for  use  on  a  submarine  boat.  The  saarchlight  shall  be  designed  with  a  special  reference 
to  quick  striking  below  decks  through  hatches  18  inches  in  diameter. 

The  projector  shall  consist  of  a  brass  drum,  Mangin  mirror,  lamp,  rheostat,  two  sockets,  front 
door  with  glass  strips,  signal  shutter  with  operating  levers,  connecting  cable,  and  tool  box. 

Each  S3irchlight  shiU  be  supplied,  among  others,  with  spare  parts  as  follows:  Twenty-five 
pairs  of  carbons  in  tin  box,  all  to  be  in  accordance  with  latest  specifications  issued  by  the  Navy 
Department. 


96  THE  SEARCHLIGHT. 

A  diagram  of  actual  connections  shall  be  pasted  or  otherwise  securely  attached  inside  the 
cover  of  the  tool  box.  This  diagram  shall  be  shellacked  or  othenrise  suitably  protected  against 
the  weather. 

CONNECTIONS. 

Two  cables  connecting  the  lamp  and  sub-base  shall  be  brought  into  drum  in  weatherproof 
manner  and  into  trunnion  base  through  water-tight  stuffing  boxes.  A  flexible  type  National  Elec- 
trical Code  cable  may  be  used.  Stufiing  boxes  shall  be  of  J-g-inch  size.  An  11,340  c.  m.  armored 
twin  conductor  cable  conforming  to  specifications  15Clb  shall  be  led  into  sub-base  through  an  anti- 
kink  spring,  terminal  tube  and  securing  clamp  in  a  manner  such  that  sub-base  will  be  water-tight 
and  searchlight  may  be  lowered  by  the  cable.  It  will  be  10  feet  long,  and  coupling  or  plug  need 
not  be  supplied. 

eiQNAL   SHUTTER. 

The  signal  shutter  shall  be  of  the  Venetian-blind  tj-pe,  easily  operated  with  one  hand  and  held 
normally  closed  by  a  spring,  but  capable  of  being  locked  open. 

Handle  shall  be  mounted  on  right-hand  side  facing  rear  of  searchlight. 

The  effective  opening  shall  be  not  less  than  S]/g  inches  in  diameter. 

It  shall  be  so  mounted  on  the  front  of  searchlight  as  to  prevent  possibility  of  leakage  of  light. 

The  leaves  of  the  shutter  shall  be  as  light  as  possible  consistent  with  strength. 

All  parts  shall  be  made  of  non-corrodiblo  material. 

The  signal  shutter  shall  be  easily  removed  from  and  replaced  on  the  front  of  searchlight. 

Each  searchlight  shall  be  supplied  with  a  signaling  shutter  unless  otherwise  specified. 

SPARE  PARTS  FOR  LOW-POWER  SEARCHLIGHTS. 

The  following  list  of  spare  parts  for  low-power  searchlights  is  the  one  upon 
which  the  supply  of  spare  parts  to  all  24  and  30  inch  low-power  searchlights  is 
based.  Slight  departures  from  this  list  occur  in  the  different  sizes  and  in  lights 
supplied  by  different  manufacturers.  The  list  as  given,  however,  gives  one  an 
excellent  idea  of  what  his  spare-part  searciilight  equijimcnt  should  be. 

One  set  of  the  following  spares  should  be  supplied  with  each  searchlight: 

WHEN    BLECTBIC   CONTROL   IS   USED. 

1  electric  controller. 

100  feet  controller  cable  with  half  couplings  attached. 

1  canvas  cover  for  projector. 

1  rheostat  for  projector — fixed  resistance. 

1  rheostat  adjustable  resistance. 

1  tool  box. 

TOOL    BOX   FOR   RATCHET-FEED   LAMPS. 

1  pair  blue  go;;gle3. 
1  pair  carbon  tongs. 
1  focusing  wrench. 

1  carbon  clamp  wrench. 

2  small  wrenches  for  8-32  and  10-32  nuts. 
2  small  wrenches  for  12-24  nuts. 

1  spanner  wrench. 

2  side  sight  glasses. 
1  chamois  skin. 

1  large  dust  brush. 
1  small  dust  brush. 

1  set  positive  and  negative  carbon  clamps  with  clamping  screws  and  washers. 

2  feeding  magnet  contact  screws. 
2  feeding  magnet  contact  springs. 
1  feeding  magnet  armature  spring. 


THE   SEABCHUGHT.  97 

2  pilot  magnet  armature  springs. 

2  pawl  springs. 

1  vertical  peep  sight  glass. 

1  complete  set  of  mica  insulation  for  lamp. 

1  set  (4)  brushes  for  elevating  motor  (when  used). 

1  set  (4j  brushes  for  training  motor  (when  usedV 

1  spirit  level. 

3  rheostat  bushings. 

TOOL   BOX   FOR    MOTOR-FEED   LAMPS. 

2  sets  carbon  brushes. 

1  brush-holder  complete. 

3  brush-holder  springs. 

1  set  brush-holder  stud  bushings. 
(These  in  addition  to  all  other  parts  listed  above  except  those  applicable  only  to  ratchet-feed 
mechanisms). 

LIST   OK   SPARE    PARTS,  HATCHET-FEED   LAMPS. 

1  complete  lamp  in  box. 

1  set  (13j  contact  fingers  for  elevating  and  training  motor  controllers. 

I  set  (10)  contact  plungers  and  springs  for  controller  contact  drums. 

1  set  (12)  armature  spools  for  pilot  motor. 

1  set  (2)  field  spools  for  pilot  motor. 

1  set  (2)  field  coils  for  elevating  and  training  motors. 

1  set  plain  front  door  strips  in  box. 

250  positive  carbons. 

250  negative  carbons. 

LIST   OF   SPARE    PARTS,  MOTOR-FEED   LAMPS. 

1  armature  complete  with  commutator  and  shaft. 
1  field  coil  of  each  size  and  kind. 
(These  in  addition  to  all  other  parts  Listed  above  except  those  applicable  only  to  ratchet-feed 
mechanisms.) 

DESCRIPTION  OF  GENERAL  ELECTRIC  CO.  RATCHET  FEED  FOR  CARBONS. 

The  General  Electric  Co.'s  ratchet  feed  for  carbons  of  searchlights  operates 
as  follows : 

The  carbons  are  fed  in  both  directions;  that  is,  both  carbons  approach 
each  other  or  draw  away  from  each  other.  Regulation  is  dependant  upon  the 
arc  voltage. 

In  this  lamp  the  series  or  striking  magnet  is  dispensed  with,  and  the  feed- 
ing magnet,  which  actually  rotates  the  feed  screws,  is  connected  across  the 
supply  circuit  to  the  training  motors  so  as  to  have  a  constant  supply  of  power. 

With  this  typo  of  lamp  it  is  necessary  to  provide  full  line  voltage  at  the 
terminals  of  the  feeding  magnets,  as  the  arc  voltage,  when  the  arc  is  first 
established,  is  about  .30  volts,  although  this  is  rapidly  increased  by  the  feeding- 
apart  mechanism.  It  will  thus  be  seen  that  feeding  magnets  which  would 
operate  satisfactorily  at  the  low  arc  voltage  would  be  injuriously  heated  by  the 
full  line  voltage  which  is  present  before  the  arc  has  been  esta1)lished,  and  the 
necessity  of  designing  the  feeding  magnets  for  the  full  line  voltage  is  apparent. 

66438—18- — 7 


98  THE  SEAECHUQHT. 

The  feeding  magnets  are  equipped  with  two  armatures  rotating  the  feed  screws 
in  opposite  directions. 

These  armatures  are  selectively'  operated  ami  controlled  by  pilot  magnet 
connected  by  means  of  links  to  steel  latches  which  lock  and  unlock  the  feeding 
magnet  armatures.  To  understand  the  operation  of  the  lamp  and  the  func- 
tions of  the  several  parts,  let  us  go  through  a  cycle  of  operation. 

After  the  carbons  have  been  inserted  in  the  clamps  and  separated  a  shght 
amount  by  means  of  the  hand  feed  wrench,  which  may  be  inserted  through 
an  opening  at  the  rear  of  the  projector,  to  engage  with  the  nut  at  the  end  of 
the  positive  feeil  screw,  the  main  line  switch  should  be  thrown  in,  making  sure 
that  the  socket  wrench  for  hand  feed  has  first  been  removed,  as  if  it  is  left  in 
engagement  with  the  feed  screw  it  causes  an  umiecessary  load  on  the  feeding 
magnets. 

Consider  the  observer  to  be  facing  the  ratchet  end  of  the  lamp  and  refer 
to  right  and  left  handed  parts  from  tliis  point  of  view. 

As  soon  as  the  main  switch  has  been  thrown  in,  the  fuU  hne  voltage  will 
be  thrown  across  the  opening  between  the  carbons,  and  consequently  across 
the  shunt  terminals  of  the  pilot  magnet,  which  is  connected  nci'oss  the  car- 
bon holders.  This  causes  maximum  flux  through  the  pilot  magnet,  attract- 
ing both  the  right  and  left  handed  armatures.  The  right-hand  armature,  on 
being  attracted,  releases  the  right-hand  feeding  magnet  armature,  causing  the 
carbons  to  be  fed  together,  the  left-hand  feedmg  magnet  armature  being 
locked  by  the  attraction  of  the  left-hand  magnet  armature.  The  carbons  now 
feed  together  until  they  touch,  at  which  instant  current  passes  through  the 
series  coil  of  the  pilot  magnet  which  is  connected  differentially  with  respect  to 
the  shunt  winding  and  reduces  the  flux  tlirough  the  pilot  magnet  to  a  minimum, 
the  voltage  on  the  shunt  winding  of  the  pilot  magnet  being  reduced  to  about 
30  volts  when  the  carbons  first  touch.  Due  to  the  reduced  flux  through  the 
pilot  magnet,  both  pilot  magnet  armatures  are  released.  This  locks  the  right- 
hand  or  feeding-together  armature  of  the  feeding  magnet  and  releases  the  left- 
hand  or  feeding-apart  armature,  resulting  in  the  separation  of  the  carbons. 

When  the  voltage  of  the  arc  has  reached  approximately  60  volts,  with 
normal  current  of  110  amperes  flowing,  the  flux  through  the  pilot  magnet  has 
increased  a  sufficient  amount  to  attract  the  left-hand  pilot  magnet  armature, 
locking  the  feeding-apart  armature  of  the  feeding  magnet.  Under  normal 
conditions  of  60  arc  volts  and  a  current  of  110  amperes  both  feeding  magnet 
armatures  will  be  latched  and  the  lamp  will  cease  to  feed. 

When  the  carbons  have  l)urned  away,  reducing  the  current  and  increasing 
the  arc  voltage,  the  flux  tlirough  the  pilot  magnet  becomes  sufficiently  strong 
to  attract  the  right-hand  armature,  thus  releasing  the  right-hand  feeding  magnet 
armature,  feeding  the  carbons  together  until  normal  conditions  of  arc  voltage 
and  current  have  been  reached.  It  ^nll  thus  be  seen  that  an  increase  in  arc 
voltage  above  normal  increases  the  flux  through  the  pilot  magnet,  releasing  the 
feed-together  armature  of  the  feeding  magnet  and  restoring  normal  conditions 
of  arc  voltage  and  current.  A  decrease  in  the  arc  voltage  reduces  the  flux 
through  the  pilot  magnet,  releasing  the  left-hand  armature  and  also  the  left- 
hand  feeding  magnet  armature,  feeding  the  carbons  apart  and  restoring  normal 
conditions  at  the  arc. 


THE   SEAECHUGHT. 


99 


^Section  A'A 

•■     a-a 

"       C'C 

-H      "       D'Q 


Fig.  109. — Cormections  of  pilot  motor  for  type  EC  projections,  Form  N. 


rig.£ 


FiqNaS 
fiolaniies  ahdPosifu 
QfriddforPos-NoJl 


Fig  No  I A  FigNo.lB 

Teit  each  Coilas  indicated  m  Fig.  No  lAffith    compass 

Thugircs    North  Armature  pole  fti(h  Current  flowing 

as  indicated  t>y  arroivs  Connect  Coifs  on  each  Pole 

as  shown  in  Fig  No  1 8  giving  Norf^/irmature  Pole 

with  Current  flawing  as  indicated 

Fig.  110. — 3&-mch  electric  coutrol  projettor,  Form  N-2.    Wiring  of  base. 


100  THE  BEARCHUGHT. 

ADJUSTMENT. 

The  lamps  are  carefully  tested  and  adjusted  before  leaving  the  factory, 
and  no  changes  should  he  made  in  the  adjustment  unless  the  arc  voltage  is  not 
maintainetl  at  approxinnitelj'  60  volts. 

In  adjusting  the  lamp  the  feed-apart  or  left-hand  armature  of  the  pilot 
magnet  should  l^e  ailjusted  by  means  of  i)ressurc  of  the  spring  (Q),  so  that  it 
will  be  released  when  the  arc  voltage  has  reached  45  volts,  feeduig  apart  until 
it  is  attracted  at  52  volts.  In  adjusting  either  of  these  pilot  magnet  annatures 
the  other  should  be  held  in  a  position  where  it  will  lock  its  feeding  magnet 
armature. 

The  feed-together  armature  of  the  pilot  magnet  should  be  adjusted  by 
means  of  pressure  on  its  spring  so  that  it  wiU  be  attracted  at  62  volts,  feeding 
together  until  54  volts  have  been  reached. 

The  jaws  of  the  latches  should  be  kept  clean  and  occasionally  a  very  small 
amount  of  good  clock  oil  should  be  applied.  Current  for  the  feeding  magnets 
enters  and  leaves  the  lamp  through  the  small  contact  shoes  while  the 
main  arc  current,  which  also  passes  through  the  series  coil  of  the  pilot  mag- 
net, and  the  current  for  the  shunt  winding  rtf  the  pilot  magnet  enters  and 
leaves  the  lamp  through  the  large  contact  shoes. 

The  mechanism  of  the  lamp  should  be  kept  clean  and  free  from  carbon 
dust  and  the  points  of  the  feeding  magnet  contact  screw  should  be  kept  clean. 

DESCRIPTION    OF    CARLISLE    <fe    FINCH    MOTOR    FEED    FOR    CARBONS. 

Several  years  ago  the  Carlisle  &  Finch  Co.  developed  a  motor-opera  teil 
mechanism  for  feeding  searchlight  carbons.  This  mechanism  is  radically 
different  from  the  ratchet  feed  used  by  the  General  Electric  Co.  in  their  low- 
power  soarclilights. 

The  Carlisle  &  Finch  feed  is  direct  motor  operated  and  consists  of  a  frame 
carrying  two  sliding  carriages.  The  positive  carbon  holder  and  supports  is 
attached  to  one  carriage.  The  negative  carbon  holder  to  the  other  carriage. 
Each  carriage  is  moved  along  slide  rods  by  means  of  a  right-hand  screw- 
threaded  shaft. 

Each  carriage  has  a  movement  of  approximately  7  inches.  The  negative 
carriage  moves  forward  awaj-  from  the  mirror.  The  positive  carriage  moves 
toward  the  mirror.  Each  carriage  is  on  a  separate  pair  of  slide  rods,  one 
above  the  other.  Each  is  actuated  by  a  separate  screw  shaft.  The  two  screw 
shafts  are  connected  together  by  gear  wheels  of  equal  size  so  that  one  revolves 
right  hand  and  the  other  left  hand.  The  lower  screw  shaft  is  driven  by  a 
worm  gear  from  the  motor,  the  upper  screw  shaft  is  driven  through  the  above- 
mentioned  gears  from  the  lower  shaft.  ^Yhen  the  motor  armature  revolves, 
the  carbon  holders  are  fed  together  or  away  from  each  other  according  to  the 
way  the  motor  revolves. 

The  carbons  burn  in  a  ratio  of  1  to  1 ,  and  hence  this  type  of  feed  is  appli- 
cable to  searchlights  using  carbons  of  this  kind. 

Figure  111  shows  the  wiring  diagram.  The  connections  are  so  arranged 
that  the  only  point  at  which  a  circuit  is  broken  is  at  the  solenoid  controller 
contacts.     Reversal  and  stoppage  of  the  motor  is  accomplished  as  follows: 

Each  pole  of  a  two-pole  field  has  upon  it  four  windings  connected  as  shown. 
These  windings  are  energized  or  de-energized  in  such  a  way  as  to  cause  the 


^  loll  for  SM/er  - 


Ssrre/Sfie&as 

Trunnion ■ — 

ifoMk^ngelShulter 
ffoai Boor  Strips  — 
3hi/l/er  Learec 
6liu/f;rfiin:j:t 


Lamp  Trough  Door 


tiTlicui'ir-Jimnq  - 
Mff/ni0/sm  Box 


Turn/ad/e 


Con/roller  Cai/ePJut 


'ff  y^ij/i/a/nr 


fyeSo/f  fur  Trunnien 

SideSKiM 
Cipfor/lrm 
IJiumSiieef  Hf/a/ 
trml/dqh/l 


ffslfom  TrmqhVenfiMor 


Coyer  f^rVeri 
Mfc/>anisinc:i 


Yfrticairraimnqif'jndW/ieet 
.[7mpCsiffS 


Cii/p/inq  i'ap 


FIG.     108.— PARTS    OF    THE    36-INCH     ELECTRIC    CONTROL     PROJECTOR,     FORM     N-2. 

FRONT    VIEW. 


THE   SEABCHLIGHT. 


101 


field  to  be  in  one  direction  or  the  other,  or  to  completely  neutralize  each  other, 
destroying  the  field  between  ends  of  poles,  thus  stopping  the  motor.  At  no 
time  during  the  entire  operation  are  the  field  circuits  broken:  instead,  cods 
are  short-circuited,  and  hence  no  current  flows  through  the  winding  so  shorted. 


Fig.  111.— Carlisle  &  Finch  Co.  motor  feed  for  carbons.    General  wiring  diagram. 


The  operation  of  this  type  of  feed  for  carbons  may  be  traced  out  from  the 
general  wu-ing  diagram.  This,  however,  is  difiicult,  and  to  simplify  explana- 
tion and  make  it  more  thorough,  additional  diagrams  are  given.  Circuits 
carrying  current  are  shown  in  solid  lines;  those  not  carrying  current  are  shown 
in  dotted  lines. 

Suppose  the  carbons  to  be  far  apart  when  line  switch  is  closed.  It  is 
obvious  that  to  establish  the  correct  length  of  arc  the  carbons  must  first  feed 


102 


THE   SEABOHLIGHT. 


together  until  they  touch  to  strike  the  arc,  and  then  feed  apart  until  the  arc 
is  drawn  to  normal  length.     This  operation  will  now  be  traced  in  detail. 

Referring  to  the  diagram  in  figure  112,  when  the  line  switch  is  closed  the 
voltage  across  carbon  tips  is  equal  to  full  line  voltage.  The  solenoids  on  the 
solenoid  controller  are  connected  directly  across  the  arc,  and  hence  a  strong 
current  flows  through  solenoid  coils  energizing  them  strongly  and  drawing  in 


Via.  112.— Carlisle  Si  Finch  Co.  motor  feed  for  carbons,  current,  flux,  and  motion.    Piagrnm  \>  ith  long  arc. 

the  plungers.  The  plungers  are  attached  to  a  brass  plate  carrying  a  contact 
at  upper  end.  This  plate  is  drawn  toward  solenoids  against  the  action  of  a 
spring,  and  contactor  on  brass  plate  makes  contact  with  contact  (B)  (top  of 
solenoid  controller).  Current  then  flows  from  positive  line  (a)  which  connects 
to  positive  carbon,  to  motor  armature,  through  armature  and  to  (b).  At  (b) 
current  divides,  flowing  partly  up  through  coil  3  on  left  field,  then  thiough 


THE   SEABCHLIGHT. 


103 


coil  3  on  right  field,  then  through  2  on  right  field  and  on  to  2  -on  left  field,  from 
which  coil  it  returns  to  the  negative  line  through  the  collector  rings  as  shown. 
The  other  part  of  current  flowing  down  from  (b)  goes  through  contact  (B)  on 
solenoid  controller  and  on  to  coil  1  on  right  field  and  then  through  coil  1  on 
left  field  and  returns  to  ne^tive  line  as  shown.     Coils  4  right  and  4  left  carry 


Fia.  U3.— Cdilisle  &  Finch  Co.  motor  feed  for  carbons,  current,  flux,  and  motion.    Diagram  with  short  arc. 

no  current  as  potential  across  these  coils  is  zero;  that  is,  they  are  short-circuited. 
The  direction  of  magnetic  field  caused  by  each  individual  winding  is  shown  by 
arrows.  On  right  field  there  are  two  Norths  and  one  South,  therefore  the 
resultant  polarity  is  North;  similarly  the  resultant  field  on  left  is  South.  The 
motor,  therefore,  revolves  in  the  direction  shown,  feeding  the  carbons  together 
until  they  touch. 


104 


THE   SEABCHLIQHT. 


Refer  now  tc>  figure  113.  The  carbons  have  come  together,  and  the  poten- 
tial across  the  arc  is  therefore  zero  and  tlie  solenoids  on  solenoid  controller  are 
no  longer  energized.  The  sjjriiig  on  brass  plate  pidls  plate  to  right,  drawing 
plungers  out  of  solenoids  and  brhiging  contact  point  on  end  of  plate  in  contact 
with  contact  point  A.     The  current  then  Ho^^'s  thrtiugh  coils  as  follows:  First, 


Normot      Afc 


e 


t^a 


© 


finushes 
.vlovab'a 
Bms* 


Rings  in 
Fik<d    Bos« 


Sola-noid  ConiToi  Jrr- 


Noi-a 


<ir«     chou/n       do++c<J 
© —-* 


lug 


Rhaoeta-f 


Line  t/oHn^e 


FiQ.  U4.— Carlisle  &  Finch  Co.  motor  (ted  (or  i  arbons,  ciirreiit,  (lux,  and  motion.     Diagram  with  normal  arc. 

from  positive  line  at  (a)  througli  armature  in  same  direction  as  before;  ajui  on 
to  (b),  where  current  again  divides,  going  this  time  partly  up  tlirough  coil  1 
left,  then  4  right,  then  1  right  and  1  left,  and  then  back  to  negative  line,  as 
before.  The  other  part  of  current  flows  down  from  (b)  and  through  solenoid 
controller  contacts,  then  up  through  coil  2  right  and  2  left  and  back  to  nega- 
tive line.     In  this  case  coils  3  right  and  3  loft  are  short-circuited  and  inactive. 


THE   SEAECHLIGHT.  105 

Polarity  of  coils  1  and  2  remain  the  same  as  before,  neutralizing  each  other  on 
each  side;  the  effect  of  coils  3  is  removed  and  an  effect  of  opposite  polarity  is 
substituted  when  coils  4  are  energized.  This,  therefore,  reverses  the  polarity 
of  the  resultant  field,  making  right  pole  South  and  left  pole  North.  Since  the 
current  in  the  motor  is  in  the  same  direction  as  before,  and  the  direction  of 
resxiltant  field  is  opposite  to  previous  direction,  the  direction  of  rotation  of 
motor  is  reversed  and  carbons  begin  to  feed  apart. 

Refer  now  to  figure  114.  As  the  carbons  are  fed  apart  the  voltage  across 
the  arc  constantly  increases.  At  the  same  time  the  voltage  across  solenoids 
on  solenoid  controller  increases,  they  being  connected  across  the  arc,  as  does 
the  current  through  them,  increasing  the  puU  on  plunger  until  it  becomes 
strong  enough  to  overcome  pull  of  spring  on  plate.  Tliis  is  adjusted  to  occiu- 
when  the  arc  is  of  normal  length.  When  this  occurs,  the  contact  on  brass  plate 
is  balanced  between  contacts  A  and  B  and  current  flows  as  follows :  from  positive 
line  running  to  carbons  at  (a)  as  before,  through  armature,  and  on  to  (b);  at 
(b)  current  flows  up,  part  going  through  coil  4  left,  then  4  right,  then  1  right, 
then  1  left  and  back  to  negative  line.  The  other  part  of  current  flows  through 
coil  3  left,  then  3  riglit,  then  2  right  and  on  to  2  left,  from  which  coil  it  returns 
to  negative  line.  It  will  be  seen  that  on  each  pole  piece  the  coils  are  half  of 
one  polarity  and  half  of  the  opposite  polarity,  the  effect  then  is  to  neutralize 
each  other  and  produce  a  resultant  field  of  zero.  Even  though  current  flows 
tlirough  armature,  there  is  no  rotation,  and  carbons  remain  at  rest  until  they 
burn  off.  When  this  occurs,  the  arc  voltage  rises,  solenoids  overcome  pull  of 
spring,  and  contact  point  on  brass  plate  is  brought  again  to  B  and  carbons 
are  fed  together  until  normal  length  of  arc  is  reached.  This  goes  on  as  long  as 
the  searchlight  is  in  operation. 

Tlie  Carlisle  &  Finch  carbon  feed  mechanism  is  excellent  and  gives  almost 
no  trouble;  it  operates  smootiily,  easily,  accurately,  and  is  seldom  in  need  of 
repair  or  attention. 

Care  must  be  taken  when  recarboniug  to  set  carbons  so  that  there  is 
about  ^  inch  space  between  the  two  carbons.  It  must  also  be  seen  to  that  the 
carbon  carriages  arc  not  jammed  against  the  end  of  travel. 

It  is  advisable  to  separate  the  carriages  by  means  of  the  socket  wrench 
to  the  full  length,  and  then  give  the  wrench  a  liaK  turn  in  the  opposite  direction 
to  prevent  jamming.  If  the  standard  length  carbons  are  used,  the  crater  of 
the  positive  wiU  be  very  close  to  the  focus  of  the  mirror.  Focusing  is  provided 
for  by  means  of  a  screw  and  handwheel,  so  as  to  bring  the  arc  in  the  proper 
focus  of  the  mirror. 


CHAPTER  9. 
SIGNALING  APPARATUS. 


12-INCH  ARC  SIGNAL  SEARCHLIGHT. 

The  arc  signal  searehlii^ht  has  been  designed  and  developed  with  a  view 
to  making  it  particularly  a(lai)tab]c  for  signal  use  on  the  bridges  and  masts 
of  ships.  It  is  arianged  for  mounting  on  stanchions  by  means  of  clamps 
and  may  readily  be  moved  from  place  to  place.  Gun  sights  or  telescope  sights,  or 
both,  are  provided  in  order  that  the  operator  may  know  definitely  when  the 
beam  is  on  the  ship  to  which  he  is  signaling. 

Signaling  is  done  in  the  usual  way  by  means  of  a  Venetian-blind  shutter 
attached  to  the  front  of  the  searchlight  barrel. 

Tlie  searchlight  is  similar  to  the  usual  12-inch  searchlight,  the  only  difTer- 
ence  being  that  the  sighting  de%'ices  are  attached  and  that  a  handle  for  elevating 
is  supplied  on  some  types  of  these  lights.  ITie  signaling  range  of  the  12-inch 
arc  signal  searc^lilight  is,  in  clear  weather,  about  9  miles  by  day,  and  about  16 
miles  by  night. 

12-INCH  INCANDESCENT  SIGNAL  SEARCHLIGHT. 

The  12-inch  incandescent  signal  searchlight  is  used  extensively  in  place 
of  the  12-inch  arc-signal  searchlight  because  of  its  greater  portability  and 
ease  of  operation,  and  because  its  construction  is  so  much  simpler  and  less 
liable  to  cause  trouble. 

It  consists  of  a  gas-filled  incandescent  lamp  mounted  at  the  focus  of  a 
parabolic  mirror,  and  the  whole  mounted  in  a  metal  barrel.  A  key  is  provided 
for  blinking.  A  condenser  is  connected  in  parallel  with  the  key  to  cut  down 
sparking  at  the  contact  points  of  the  key.  Provision  is  made  for  mounting 
on  a  stanchion  or  on  the  bridge  rail.  A  telescope  and  gun  sights  are  pro- 
vided to  enable  the  operator  to  hold  the  beam  on  the  receiving  ship. 

The  signaling  range  of  the  12-inch  incandescent  signal  searchlight  is 
about  2§  miles  by  day  and  7  to  10  miles  by  night. 

FoUow'ing  are  specifications  for  the  12-inch  incandescent  signal  search- 
light, and  a  copy  of  the  test  on  one  manufacturer's  light: 

Specifications  for 
Standard  Incandescent  Lamp  Sionalinq  Searchliorts 

FOR 

Use  in  the  United  States  Navt. 

IJune  5,  1817.) 

1.  General  instructions. — Goaoral  specifications  for  the  inspection  of  material  issued  by 
the  Nav\'  Department,  in  effect  at  the  date  of  opening  of  bids,  shall  form  a  part  of  these  specifi- 
cations. 

106 


FIG.     115.— CARLISLE    &    FINCH     12-INCH    ARC    SIGNAL    SEARCHLIGHT.       THREE-QUARTER    BACK 
VIEW.     SEARCHLIGHT    ARRANGED    FOR    STANCHION    MOUNTING. 


^i^ywlf 


mm^^- 1 


FIG.     llf.a.— CARLISLE     &     FINCH     12-INCH     ARC     SIGNAL     SEARCHLIGHT.       SHUTTER     REMOVED. 

THREE-QUARTER    FRONT    VIEW. 


FIG.    116. -VENETIAN     BLIND    SIGNAL    SHUTTER    CLOSED, 


FIG.    117.— VENETIAN    BLIND    SIGNAL   SHUTTER   OPEN. 


THE   SBAEOHUOHT. 


107 


2.  The  searchlights  will  be  designated  by  the  following  types: 
Type  A:  Standard  (manufactured  of  non-magnetic  material). 
Type  B:  Standard  (manufactured  of  steel). 

All  types  will  be  designed  for  operation  with  any  of  the  following  lamps  which,  however,  will 
not  be  supplied  with  searchlights. 


WEIGHT    OF    SEARCHLIGHT IIO  POUNDS 

Fio.  118.— Carlisle  &  Finch  Co.  12-inch  arc  signal  searchlight.    Stanchion  mounting. 

(a)  Stereopticon  Mazda  ?,  200-watt,  125-volt,  skirted  medium  screw  base  (5i  inches  overall 
length). 

(6)  Stereopticon  Mazda  C,  •500-watt,  125-volt,  skirted  medium  screw  base  (7^  inches  overall 
length). 

(c)  Concentrated  filament  Mazda  C,  fi- volt,  108-watt  (6  inches  overall  length),  skirted  medium 
screw  base. 

(rf)  Concentrated  filament  Mazda  C,  12-volt,  120-watt  (6  inches  overall  length),  skirted 
medium  screw  base. 


108 


THE  SEARCHLIGHT. 


(«)  Concentrated  filaraont  Mazda  C,  24-volt,  150-watt  (6  inches  overall  lengthy  skirted  medium 
screw  base. 

(/)  Concentrated  filament  Mazda  C,  30-volt,  150-\vatt  (6  inches  overall  lonfrth\  medium 
screw  base. 

3.  Description. — Each  searchlight  will  consist  of  barrel,  glaas  mirror,  lamp  socket,  signaling 
key,  condenser,  two  st^ts  clamps  for  securing  to  st;uichions,  and  10  feet  of  No.  10  Brown  ik  Sharpe 
gauge  plain  bniid  .National  Electrical  Code  portable  cable.  All  searclilighta  will  be  wired  up 
complete,  ready  tor  uso,  with  exception  of  plug,  wliich  need  not  be  supplied.  The  general  outline 
of  searchlight  will  be  shown  on  sketch  forming  part  of  these  specifications 

4.  Barrel.— The  barrel  will  be  of  sheet  metal  at  least  i\'o.  20  Brown  &  Sharpe  gauge  (0.032  inch) 
in  thickness.  Sheet  brass  will  be  used  for  t>'pe  A  searchlight  and  sheet  steel  for  type  B  search- 
light.    It  will  be  supported  in  an  approved  manner  by  clamps  as  boreinafter  described.     It  will 


LAMt 


rOi 


B 


w  ic?  ifM  a 


Fio.  119. — 12-inch  incaodcscent  signal  searchlight,  showing  mounting  and  wiring  diagram. 

be  sufficiently  ventilated  to  prevent  injury  to  the  mirror  from  heat  when  operated  continuously 
for  four  hours  indoors.  A  suitable  handle  at  back  of  barrel  will  be  provided.  The  barrel  will 
be  capable  of  free  movement  of  at  least  45°  above  and  below  horizontal,  and  a  free  movement  of 
the  entire  circle  in  the  horizontal  plane.  Suitable  means  mil  be  pro\'ided  for  locking  the  barrel 
in  any  desired  position  in  the  vertical  and  horizontal  planes.  The  barrel  will  contain  an  incandes- 
cent lamp  socket  and  parabolic  reflecting  mirror,  in  accordance  with  paragraph  5  of  these  specifica- 
tions, and  will  be  fitted  with  a  glass  weatherproof  front  door,  hinged  on  one  side  and  secured  on 
the  other  side  by  a  suitable  clamp  to  provide  easy  access  for  removal  of  lamp.  Heat-resisting  glass 
will  be  installed  in  front  door.  Arrangements  will  be  made  for  the  adjustment  of  lamp  in  focus 
by  means  of  a  thumb  screw  or  other  suitable  method  from  the  e.xterior  of  barrel. 

A  sighting  arrangement  consisting  of  two  suitable  gun  sights  mounted  on  right-hand  side  of 
barrel  facing  mirror  will  be  provided. 


THE   SEARCHLIGHT. 


109 


5.  Mirror. — The  mirror  will  be  parabolic  and  in  strict  accordance  with  specifications  17-M-3a 
of  February  1,  1917.  ^Miere  mirror  is  not  manufactured  by  bidder,  the  bureau  will  be  informed 
in  bid  the  name  of  the  firm  manufacturing  same  and  also  supplied  with  a  copy  of  contract. 

6.  Securing  clamps. — The  securing  clamps  will  be  in  the  form  of  a  socket  and  pivot.  The 
socket  will  be  provided  with  a  nonremovable  thumb  screw  which  will  easily  and  effectually  clamp 
the  searchlight  by  friction  in  any  desired  position.  The  stanchion  clamping  arrangement  will 
be  adjustable  for  stanchions  varying  from  1}  to  SJ  inches  in  diameter.  The  pivot  will  operate 
freely  and  be  mechanically  secured  by  a  quick  releasing  arrangement  in  the  socket  so  arranged 
that  the  searchlight  can  be  lifted  from  the  socket.  Two  sockets  w  ill  be  supplied  for  each  search- 
light. The  clamps  for  type  A  searchlight  will  be  of  uormiagnetic  material.  The  clamps  for  type 
B  searchlight  will  be  of  cast  steel  or  other  approved  material. 

7.  Operating  key. — Means  \rtll  be  pro\  ided  for  the  operation  of  searchlight  with  an  approved 
blinker  key  and  condenser  which  will  be  inclosed  in  a  light  splash-proof  key  box,  secured  to  the 


TZLLGftfiPH  KEY 
AND  CONSlfiitR 
IN  CASe 


Fig.  129. — Crouse-Hinds  12-inch  incandescent  signal  searchlight,  showing 
method  of  mounting  on  rail. 

searchlight  support.    Material  for  type  A  searchlight  will  be  non-magnetic.     Material  for  type  B 
searchlight  will  be  steel  or  other  approved  material. 

8.  Bushings. — Each  searchlight  and  key  box  will  be  equipped  with  bushings  capable  of 
talking  a  No.  10  B.  &  S.  gage  N.  E.  code,  plain  braided  cable 

9.  Lamp  socket. — Lamp  socket  will  be  for  Edison  medium  screw  base,  and  if  of  suitable 
design  may  be  of  porcelain. 

10.  Material. — All  material  of  searchlight  type  B  will  be  thoroughly  sheradized  to  prevent 
corrosion. 

11.  Approval  of  type. — The  searchlight  will  be  constructed  throughout  with  a  view  to 
lightness  without  sacrificing  strength  and  ruggedness.  It  shall  be  of  a  type  which  has  been  demon- 
strated by  test  to  be  satisfactory  for  the  service  intended.  In  the  event  that  the  type  proposed  to 
be  furnished  has  not  been  tested  by  the  Bureau  of  Steam  Engineering,  a  sample  of  searchlight 
will  be  forwarded  to  the  navy  yard,  New  York,  for  test     The  sample  submitted  need  not  be  com- 


110 


THE  ftBABCHUQHT. 


FiQ.  121.— The  Carlisle   &    Finch   Co.  13-lnoh   incandescent   signal   searohUght.    Pedestal 

mounting  tus  used  on  UO-foot  putrol  bonis. 


WEIGHT    OF     SEARCHUeHT  ...      42   LBS.    APPfiOX)tMT£LY 
Fig.  122.— National  X-Ray  Heflector  Co.  12-lnch  Incandescent  signal  searchllgbt.    Stanchion  mounting. 


THE  SEABCHUGHT. 


Ill 


plete  in  all  respects  to  the  requirements  of  these  specifications.  Searchlight  as  conamercially 
constructed  will  suffice  for  material  for  test,  pro\'ided  assembly  and  detailed  plans  of  outfit  to 
specification  requirements  as  proposed  are  submitted  with  samples.  Plans  will  be  in  detail  as 
called  for  under  paragraph  14. 

12.  Finish. — The  exterior  surfaces  of  searchlight  will  be  finished  in  slate  gray.  The  interior 
surfaces  of  barrel  and  back  of  mirror  \vill  be  finished  dull  black. 

13.  Name  plates. — A  name  plate  showing  manufacturer's  name  or  monogram,  serial  munber 
of  searchlight,  requisition  and  contract  number  and  date  will  be  fitted  to  the  searchlight  in  a 
conspicuous  place. 

14.  Plans. — Prior  to  placing  contract. — Unless  already  on  file  at  the  bureau,  there  wiU  be 
furnished,  in  triplicate,  with  each  proposal,  blue  print  plans  covering  the  apparatus  proposed. 


Fig.  123.— General  Electric  Co.  12-iiich  incandescent  signal  searchlight. 
Pedestal  mounting'. 

These  plans  will  include  assembly  and  details  of  all  parts,  weight  of  each  part,  materials  used , 
mirror  manufacturer's  name,  method  of  securing'mirror,  method  of  securing  and  adjusting  lamp 
socket,  actual  construction  and  connections,  etc. 

No  PKOEOSAL  WILL  BE  CONSIDERED  UNLESS  THESE  PLANS  REFERRED  TO  ABOVE  ARE  INCLUDED 
AS  PART  OF  THE  BID. 

After  placing  contract. — Unless  already  on  file  at  the  bureau  prior  to  date  for  final  delivery  there 
will  be  forwarded  to  the  Bureau  of  Steam  Engineering,  Navy  Department,  Washington,  D.  C, 
via  the  inspection  officer,  one  set  of  assembly  and  detailed  tracings  of  the  complete  outfit.  Finished 
plans  will  conform  to  the  following  sizes: 

27  by  20  inches. 

27  by  40  inches. 

27  by  60  inches. 

27  by  80  inches. 

27  by  84  inches. 
The  vertical  dimension  of  tracing  will,  in  all  cases,  be  27  inches. 


112 


THE  SEABCHUQHT. 


15.  Spare  parts. — The  following  spare  parts  will  be  furnished  with  each  searchliglit:  One 
lamp  socket,  if  of  porcelain. 

16.  Weight. — The  net  weight  of  the  apparatus  as  a  whole  and  the  principal  parts  will  be 
stated  Lu  the  proposal. 

Copies  of  this  advance  sheet  can  be  obtained  upon  application  t<j  the  Uurenu  of  St«ani  Kngi- 
neeriiig,  Navy  Department,  Washington,  D.  C. 

Report  op  Test  of  12-inch  Incandescent  Lamp  Sionauno  Searchlight  ok  Natiokai  .\-Kav 

Reflector  Co. 

1.  Tests  in  accordance  with  reference  (a)  have  been  conducted  by  this  division  on  a  s,iniple 
12-inch  incandescent  lamp  signaling  searchlight,  supplied  on  contrmt  No.  797,  requisition  R.  M.  7, 
by  the  National  X-Ray  Rellector  Co.,  to  determine  its  compliance  with  advance  sheet  :J5a  dat<'d 
March  15,  1917. 


Fio.  124. — General  Electric  Co.  12-incb  Incandescent  signal  searcliligtat.    Stanchion  mounting. 

2.  Description. — The  searchlight  consists  of  a  drum,  mounted  on  trunnion  arms,  and  fitted 
on  a  S'.rivel  w  hich  can  be  fastened  to  stanchion  aboard  ship.  A  telegraph  key.  fitted  with  necessary 
condenser  is  mounted  on  the  base  of  the  trunnion  arms.  The  back  of  the  drum  is  fitted  « itli  a  metal 
dome  within  which  is  mounted  a  glass  parabolic  mirror.  In  th<-  bottom  oi  the  drum' is  mounted 
a  sliding  plate,  in  which  is  secured  the  lamp  receptacle.  This  plate  can  be  moved  backward  or 
forward  for  the  purpose  of  focusing  the  lamp.  A  sight  tube  is  fitted  to  the  drum.  A  lock  nut  is 
furnished  on  the  plate,  by  means  of  which  the  lamp  can  be  moved  upward  and  downward  for 
focusing.  The  front-door  glass  is  a  solid  flat  plate.  The  front  door  is  hinged  on  the  side  and  fitted 
with  a  screw  clamp  for  securing  the  door  shut. 

3.  Tests. — A  250-watt  >fazda  "C"  stereepticon-type  lamp  was  mounted  in  the  searchlight 
and  the  beam  focused  as  nearly  parallel  as  possible,  and  readings  taken  of  the  intensity  of  the-  beam 
in  foot  candles  at  80  feet  from  the  searchlight.  The  results  are  shown  plotted  in  fig.  125.  A 
beam  candlepower  reading  was  then  taken  at  the  beam  center. 


THE   SEAHCHUGHT. 


113 


4.  The  mirror  was  then  removed  from  the  light  and  tested  in  accordance  with  specifications 
17-M-3a,  w-ith  the  omission  of  the  backing  test,  which  was  not  conducted  as  the  contractor  objected 
to  this  mirror  being  subjected  to  the  complete  backing  test,  as  his  understanding  when  he  accepted 
the  contract  was  that  any  mirror,  so  long  as  it  approached  a  parabolic  shape  would  be  accepted 
by  the  Navy  Department.  Under  those  circumstances  it  was  not  thought  advisable  to  apply  the 
backing  test  of  specifications  17-ll-3a,  as  it  is  thought  probable  that  this  mirror,  which  is  very 
cheaply  made  and  poorly  annealed,  will  check  and  break  if  subjected  to  any  high  temperatures. 

5.  Res^dts. — The  drum  and  lamp  moimting  are  considered  up  to  specified  requirements  and 
satisfactory  for  naval  8er\'ice. 


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Fio.  125. 


7.  Beam,  candlepower. — The  horizontal  beam  candlepower  at  beam  center  is  96,000  candle- 
power. 

8.  Condunon. — ^The  drum  and  stanchion  clamps  are  considered  satisfactory  for  naval  service, 
but  the  mirror,  the  most  vital  part  of  the  outfit,  is  considered  ver\-  inefficient,  cheaply  made, 
and  on  the  whole  unsuited  for  naval  service,  and  it  is  considered  that  lights  of  this  tj-pe  equipped 
with  inferior  mirror  should  not  be  accepted  for  naval  ser^dce. 

9.  The  beam  candlepower  is  considered  low,  showing  only  92,000  candlepower  as  compared 
with  125,000  candlepower  for  lights  of  the  same  size,  supplied  on  former  contracts,  when  using 
the  250-watt  lamp. 


66438— IS- 


-8 


114 


THE   SEABCHLICHT. 


PORTABLE  TUBE  BUNKER. 

A  portable  tube  blinker  consists  essentially  of  a  light  in  a  tube  which  is 
closed  at  one  end.  The  light  may  be  seen  only  from  a  very  small  area  directly 
in  front  of  the  open  end  of  the  tube.  Tlie  particular  advantage  of  this  piece 
of  apparatus  ii  tliat  signals  may  be  sent  from  ship  to  ship  without  tho 
flashes  being  visible  from  any  point  outside  of  the  line  of  tho  tube.  Signals 
may  therefrre  be  sent  at  night  without  danger  of  disclosing  the  position  of 
the  ships  to  the  enemy. 


CLAMf 


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nyo  CIAMP3,  ro/?  »ot.oi/\t^  aw 
0£ric£f(   or  £?£Cf<   spy  a  las%  . 


2  G' 


Fio.  120.— I'orlable  tube  blinker. 

There  are  two  general  types  of  portable  tube  blinkers— Navy  standard, 
which  is  supplied  to  regular  Navy  ships,  and  commercial  type,  which  is  supplied 
to  small  patrol  boats,  submarine  chasers,  and  merchant  ships  in  the  Navy 
service.  They  are  essentially  the  same,  although  tho  Navy  typo  is  heavier 
and  of  better  construction  than  the  commercial  type,  and  differs  in  details  of 

construction.  •    >     i 

In  both  types  there  are  two  classes— self-contained  and  "plug-m  classes. 
The  self-contained  class  (shown  in  fig.  123)  has  a  battery  in  the  base  of  the  tube 
wliich  suppUes  power  for  the  light,  while  the  "plug-in"  class  has  attached  a 


w — P 


Li! 


dT  ^C 


FIG.   127a.     ALOIS  SIGNAL  LIGHT    WITH    STORAGE    BATTERY    ANU    iPAhE    BULBS 


FIG.  12713. —FRONT   VIEW    OF   ALOIS    LIGHT. 


FIG.  127c.— METHOD   OF    USING   ALOIS   SIGNAL   LIGHT 
TO  SIGNAL  AN   AEROPLANE. 


THE   SEAKCHLIGHT.  115 

cord  and  plug  by  means  of  which  the  lamp  is  plugged  in  on  the  ships'  circuit 
and  gets  its  power  supply  from  a  source  external  to  itself. 

The  Navy  standard  portable  tube  blinker  has  on  the  tube  two  rests  on 
which  an  officer-of-the-deck  spyglass  may  be  laid  and  strapped  in  place  by 
using  the  strap  attached  to  the  spyglass.  This  provides  the  means  of  sighting. 
The  commercial  type  portable  tube  blinker  is  supplied  with  gun  sights  for  the 
same  purpose. 

The  range  of  this  blinker  is  very  short  (about  2^  miles).  It  can  be  used 
only  at  night. 

THE  21-INCH  HIGH  POWER  SIGNAL  SEARCHLIGHT. 

Recent  developments  in  naval  warfare  have  necessitated  the  supply  of 
searchhghts  for  signaling  which  have  far  greater  range  of  visibility,  and  there- 
fore a  greater  signahng  range,  than  any  signaling  searchlights  the  past. 

Ships  on  patrol  duty  against  submarines,  and  in  convoy,  and  fleets  of  large 
size  in  very  extended  formation  require  visible  signaling  apparatus  with  long 
range,  inasmuch  as  it  has  been  found  unsafe  to  use  radio  for  signaling  while 
at  sea. 

The  24-inch  high-power  searchlight,  specially  designed  for  signaling,  seems 
to  be  the  most  suitable  searchlight  for  use  imder  the  conditions  imposed  by 
present  circumstances  at  sea. 

The  first  searchlights  of  this  type  are  manufactured  by  the  Arma 
Engineering  Co.  They  wiU  be  arranged  especially  for  signal  use,  having  one- 
man  control,  a  suitable  signaling  shutter,  and  telescope  for  sighting.  The 
telescope  wUl  be  arranged  so  that  it  may  be  "bore-sighted"  with  the  beam 
of  the  searchlight. 

The  control  will  be  operated  by  two  handwheels  connected  bj"  suitable 
gearing  to  the  turntable  and  to  the  trunnion  arms.  One  handwheel  will 
operate  the  searchhght  ui  train,  the  other  in  elevation.  Tlie  rate  of  train 
will  be  10°  in  azimuth  per  revolution  of  the  training  handwheel;  rate  of  eleva- 
tion will  not  exceed  2^°  per  revolution  of  elevating  handwheel. 

The  lamp  mechanism  will  be  similar  to  that  described  in  chapter  2,  Arma 
high-power  searchhght. 

ALPIS  SIGNAL  LIGHT.      ' 

The  Aldis  signal  light  is  a  hand  signal  light  with  a  pistol  grip.  The  dots 
and  dashes  are  produced  by  pulUng  a  trigger  which  tilts  a  parabohc  mirror  and 
brings  the  searchhght  beam  to  coincide  with  the  line  of  sight  through  the 
sighting  telescope  or  tube,  which  is  mounted  on  the  barrel.  When  trigger  is 
not  pulled  the  beam  is  much  higher  than  the  line  of  sight  and  hence  not  visible 
to  anyone  on  whom  the  telescope  is  sighted.  An  incandescent  lamp  of  special 
design  is  used  in  the  hght.  It  bums  continuously  when  light  is  held  by  grip, 
the  circuit  being  closed  by  the  pressure  of  the  hand  on  a  second  trigger  on  the 
grip.     A  small  storage  battery  supplies  the  power  to  nm  the  lamps. 

This  piece  Of  apparatus  is  small,  hght,  and  efficient,  and  very  useful  for 
daylight  signaling  between  vessels  operating  near  each  other,  and  between 
aeroplanes  and  ships  or  ground.     The  weight  of  lamp  is  about  5J  poimds. 

The  illustration  will  serve  to  give  a  general  idea  of  the  light.     (Fig.  127.) 

These  lights  will  be  supphed  to  seaplanes,  naval  air  stations,  battleships, 
cruisers,  destroyers,  etc. 


CHAPTER  10. 
TYPES  OF  OPERATING  GEARS. 


DISTANT  MECHANICAL. 

The  earliest  types  of  distant  operating  systems  were  crude  and  inaccurate, 
though  rather  interesting.  One  of  the  very  earliest  emploj-ed  two  drums  at 
the  control  station;  around  them  was  wound  a  rope  drive.  This  drive  went  to 
other  drums  on  the  searchlight  which  turned  when  the  drums  at  the  control 
station  were  turned,  thus  forming  a  pulley  sj-stem  for  elevating  or  depressuig 
the  light,  or  for  training  it. 


Fia.  12j.— Searchlight  operating  gear.    I'ump-haml.e  type. 

f 

Shortly  after  this  type  was  used,  there  was  developed  the  pump-handle 
type  shown  in  sketch.     (Fig.  128.) 

The  light  was  supposed  to  follow  exactly  the  motions  of  the  controller, 
training  as  the  lever  was  turned  and  elevating  or  depressing  as  the  lever  was 
raised  or  lowered.  This,  however,  it  never  did  very  well,  and  though  used  to 
some  extent  was  never  very  satisfactory. 

The  pilot-house  type  of  control  was  found  satisfactory  for  small  lights  so 
mounted  that  this  type  of  control  could  be  used.  One  form  of  pilot-house  type 
of  control  is  shown  in  figure  129. 

The  systems  of  gearing  in  the  bases  of  scarclilights  are  interesting  and  are 
of  many  types.     A  few  are  shown  in  diagrams  and  brief  descriptions  given. 

The  system  shown  in  figure  130  is  a  development  of  the  pilot-house  type 
of  control  for  application  to  large  searchlights.     Two  shafts  are  used,  being 
connected  to  the  operating  handwheels  by  universal  joints. 
116 


THE  SEABCHUGHT. 


117 


The  light  is  elevated  and  depressed  by  a  gear  fixed  in  space  turning  about 
a  screw  shaft;  this  shaft  moves  a  crosshead  bar  which,  by  means  of  connecting 
rods  and  cranks,  tilts  the  light  on  its  trunnions.  The  training  gear  is  very 
simple  and  the  sketch  needs  no  explanation.  It  wiU  be  noted  that  as  the  lamp 
is  moved  in  train  the  elevation  changes,  due  to  the  screw  shaft  screwing  in  or 


Fio.  129.— Pilot-house  type  of  searchlight  operating  gear. 

out  of  the  surrounding  gear.  This  type  of  control  was  used  on  old  General 
Electric  Company's  searchlights. 

Another  type  of  operating  gear  used  on  the  General  Electric  Co.'s  old 
searchliglits  is  shown  in  figure  131. 

The  training  gear  is  practically  the  same  as  that  shown  in  preceding  sketch. 
The  elevating  gear  employs  a  worm  and  wheel,  the  worm  wheel  being  at  one 
end  of  a  short  shaft  and  a  pinion  at  the  other  end.  The  pinion  engages  an  arc 
rack  and  rolls  the  hght  about  its  trunnions. 


118 


THE   SEAHCHLIOHT. 


Afic  ElLSiVATiNG  Rack 


'//j^/////////////////////M^ 


NoT^.  Error  in 

£l£YATION    due 
To    Tr/]i/V 


Pio.  130. — Old  arc  rack  and  pinjon  type  of  searchlight  operating  gcai'.    Arrangement  of  geart  In  base. 


NOT£.    ERROn   i/i 
EL£VAT/ON    DUE 

TO  Training. 


EiLEVATIOt^- 


TRAIN 


Fio.  131.—"  Push  type"  searchlight  operating  gear. 


THE  6EABCHLIGHT. 


119 


In  this  light  there  is  also  a  change  in  elevation  due  to  training,  caused  by 
the  worm  wheel  revolving  about  the  worm  when  the  turntable  is  revolved. 

Concentric  shafts  are  used  in  this  type  of  operating  gear.  These  shafts 
carry  horizontal  handwheels  on  their  lower  ends,  one  for  training  and  one  for 
elevating.    This  type  of  gear  is  now  in  use  on  the  Wisconsin  and  other  ships. 

In  figure  132  is  shown  the  type  of  operating  gear  now  in  use  on  many  Beck 
(General  Electric  Co.  high  power)  searchlights.  Concentric  shafts  aro  used  in  this 
type  of  operating  gear,  the  outer  shaft  being  for  training  and  the  inner  for 
elevating.  The  gear  for  elevating  is  in  a  general  way  similar  to  the  last  gear 
described,  except  that  bevel  gears  are  used  in  place  of  worm  and  wheel  gear. 


Note.- ERROR  iN 
EuevfijioN   Due 

TO  TR/\lf/. 


H/\No  Operating  S£>ja 
(pdovioEo  wm  lock} 


EuevfiijioN 

TRfKlN 


Fia.  132. — Arrangement  of  gears  in  base  of  Beck  distant  mechanical  control.    High-powerscarchllght. 


The  training  gear  is  supplied  with  distant  mechanical  control  and  also  hand 
control  at  the  light.  Gears  A  and  B  are  provided  with  locks  which  may  be 
used  to  keep  the  wheels  fixed  against  revolving.  Gears  B  and  D,  and  A  and  C 
are  on  separate  shafts.  Gear  E  is  an  idler,  loose  on  the  elevating  shaft,  fixed 
in  space,  and  meshing  with  C  and  D. 

To  use  hand  control  at  the  light,  gear  A  is  unlocked  and  gear  B  is  locked; 
this  locks  gear  E  as  well,  so  that  when  A  is  turned,  C,  being  on  the  same  shaft, 
also  turns  and  rolls  around  E,  revolving  the  turntable. 

To  use  distant  mechanical  control,  gear  B  is  unlocked  and  gear  A  is  locked, 
so  that  there  is  possible  no  relative  motion  between  E  and  C.  Thou,  when 
training  shaft  is  turned,  D  turns  E,  and  as  E  turns,  C  is  carried  around  with  it, 
revolving  the  tiu-ntable. 


120  THE    SEARCH LlGHt. 

In  this  light  there  is  a  change  in  elevation  due  to  training,  caused  by  the 
vertical  bevel  gear  rolling  around  on  the  horizontal  gear  when  turntable  is 
revolved. 

The  Pennsylvania  is  equipped  with  this  type  of  operating  gear. 

This  type  of  gearing  may  be  arranged  to  operate  by  separate  shafts  by 
omitting  gear  B,  providing  a  lock  on  gear  D,  and  extending  shaft  carrying  D 
and  B  through  base  of  searchlight.    Some  lights  are  arranged  this  way. 

The  General  Electric  Co.  is  now  developing  a  standard  type  of  base  for  use 
with  nil  operating  stands.  Separate  shafts  lead  from  the  base  to  the  stands. 
No  drawings  of  this  base  are  available  at  present,  but  no  new  principles  are 
involved. 

Tliere  are  at  present  installed  on  ships  six  old  types  of  distant  mechanical 
controller  gears  for  scarclilights,  knowTi  respectively  as  A,  B,  C,  D,  E,  and 
General  Electric  Co.'s. 

TYPE  "A"  OPERATING  GEAR. 

Tliis  system  is  designed  to  operate  the  light  from  a  point  about  twelve  feet 
below  the  base  of  the  light.  It  provides  a  simple  and  reliable  method  of 
training  and  elevating  the  light  from  a  short  distance.  Tlie  light  is  operated 
by  turning  a  pair  of  handwheels  connected  to  the  drum  b}'  means  of  gears  and 
shaftings.  There  are  two  such  pairs  of  handwheels,  one  serves  to  elevate  the 
drum  and  the  other  to  train  it. 

Tlie  construction  of  the  elevating  controller  is  identical  with  that  of  the 
training  controller.  The  handwheel  transmits  its  rotation  to  a  vertical  shaft 
in  the  box  through  a  beveled  gear.  This  operating  gear  is  connected  to 
the  operating  mechanism  in  the  base  of  the  lamp  by  means  of  a  shaft  and 
two  universal  joints.  This  mechanism  will  be  described  later.  The  shaft  in 
the  control  box  also  carries  a  worm  which  engages  a  gear  wheel  carrying 
a  brass  disk.  The  edge  of  the  disk  carries  a  scale  of  degrees  of  arc  which  may 
be  viewed  througli  a  small  window.  A  small  electric  lamp  is  placed  above  the 
scale  so  that  i  t  may  be  illuminated  and  the  scale  read  at  all  times.  The  scale 
is  geared  to  the  shaft  in  the  same  ratio  that  the  drum  is,  so  that  the  scale 
readings  iu  the  controller  box  correspond  to  those  on  the  drum  at  all  times. 

The  mechanism  in  the  base  of  the  lamp  consists  of  gears  and  shafting 
to  transmit  the  motion  of  the  handwheel  to  the  drum.  ITie  two  operating 
shafts  come  up  through  the  base  of  the  lamp.  The  training  shaft  is  connected  to 
the  rack  on  the  rotating  part  of  thebasetlirougha  train  of  gears  and  a  short  shaft. 
One  pair  of  gears  may  be  disengaged  by  means  of  the  pedal  on  the  side  of  the 
base,  so  that  the  light  may  bo  trained  at  the  lamp.  The  handwheel  for  this 
purpose  is  geared  to  the  training  rack  at  a  point  diagonally  opposite  to  the 
remote  operating  gear.  . 

The  elevating  shaft  passes  through  the  axis  of  the  base  and  is  geared  to  a 
small  horizontal  shaft  on  the  rotating  part  of  the  base.  The  other  end  of  the 
shaft  is  under  one  of  the  ti-unnion  arms  supporting  the  drum,  where  it  is  geared 
to  another  shaft  running  along  the  trunnion  arm  to  a  point  just  under  the  drum 
bearing.  Here  it  is  geared  to  the  elevating  rack  on  the  side  of  the  drum.  This 
gear  may  be  made  to  enage  or  disengage  the  rack  by  the  small  liandle  on  the 
standard.  The  whole  mechanism  is  easily  seen  by  removing  one  of  the  handhole 
covers  from  the  base. 


4H 


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<SeneravEi£ctwc  ^C>S.TfPt 


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<SENtRAvElECTRl£  ^cJs.TfPt 


0W3^— IB     (To  (aco  piige  120.) 


FIG.   133. -TYPE    A    SEARCHLIGHT    OPERATING    GEAR    CONTROLLERS. 


THE   SEAECfiLIGHT. 


121 


The  gear  ratio  between  the  handwheels  and  drum  is  20  to  1.  With  this 
ratio  the  lamp  is  easily  handled  and  it  affords  a  sufficiently  wide  range  of 
speed  for  all  purposes. 


CR6Lt  HOUS 


0  Point  ontks 
flziMuiH  cmaE. 


Fig.  13.).— Type  A  searchllc;lit  opcraliiK;  gear  lattaclicil  to  Peek  art-inch  high-power  searchlight). 

Tlie  scale  showing  elevation  is  correct  for  only  one  position  of  train  because 
of  the  change  in  elevation  due  to  traming  the  searchlight.  It  is  possible  to 
introduce  a  gearing  between  the  two  controllers  which  will  make  the  elevation 


122 


THE   SBABCHLIQHT. 


I 

5 
I 


c 


o     Si 


I 


UJ 


S 


IT 


I" 


2d  c^ 


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C 


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D    I 

a 


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el 


1 


THE   SBABCHLiaHT. 


123 


scale  read  correct  for  all  positions  of  train,  i.  e.,  it  will  record  the  change  in 
elevation  due  to  training  (fig.  136).  This  gearing  is  not  in  use  on  any  ship 
of  the  United  States  Navy  and  is  sliown  merely  as  a  matter  of  interest. 

TYPE  "B"  OPERATING  GEAR. 

Type  B  control  is  mounted  on  a  pedestal  and  has  but  one  box  for  training 
and  elevating.  Three  handwheels  are  used,  one  on  each  of  throe  sides  of  the 
box.  Two  are  for  training  and  one  for  elevating.  Concentric  shafts  and 
universal  joints  are  used  to  connect  controller  gears  to  searchlight  base  gears. 
Scales  showing  angles  of  train  and  elevation  are  supplied,  but  the  same  fault  of 
incorrect  elevation  indication  at  all  positions  but  one  is  present  whenever  any 
gear  system  in  a  searchlight  base  is  supplied  having  gears  so  arranged  that 
elevation  changes  when  hght  is  tramed.  General  arrangement  of  type  B  con- 
troller box  is  shown  in  diagram. 


£/e.y(xtton-^ 


l^'v^^V.Wi^VV'Wv'^'v^VV.WV.V^vjJ. 


tF 


{Train 


Fig.  i:<7 


-S\stcm  of  Gearing  in  searchliKiil  tasc  for  o^  ercominy  cliauiJe  of  anple  of  elevation  of  beam  b;  traiuinR 

searchlight. 


There  has  been  devised  a  system  of  double  differential  gearing  for  concentric 
operating  shafts,  which  eliminates  the  change  in  elevation  of  searchlight  due 
to  training.  The  gears  are  located  in  base  of  searchlight.  The  principle  apphod 
to  type  B  operating  gear  is  shown  in  figure  137. 

Suppose  the  turntable  to  be  revolved  by  turning  gear  attached  to  bracket  (h') . 
The  yoke  on  (h')  connecting  to  differential  gear  (h)  goes  through  one  revolution, 
rolling  around  fixed  gear  (e).  Double  gear  (f)  then  goes  through  two  revolutions 
in  the  same  direction,  being  rotated  one  revolution  and  cari'ied  around  one  revolu- 
tion during  one  revolution  of  (h).  Yoke  (a')  then  makes  one  revolution  in  the 
same  direction,  rolling  on  (d),  which  remains  stationary.  Yoke  (a')  turns 
gear  (a)  through  one  I'evolution  in  same  direction  as  turntable.  Since  gears  (b) 
and  (c)  which  operate  elevating  rack  are  on  turntable  and  make  one  revolution 
when  (a)  makes  one  revolution,  there  is  no  relative  rotation  between  gears  (a) 
and  (b)  and  hence  no  motion  is  transmitted  to  elevating  rack. 


124 


THE   6EAKCHLIGnT. 


This  system  is  not  m  use  at  present  because  there  is  no  system  of  operating 
gear  in  use  sufficiently  refined  to  warrant  it. 


^^''^'f^'t^-^ 


C^^BLC  ffOL£S>. 


Fio.  13».— Type  I> searchllRht  opcratinRgcar  (aitachcd  to  necV  Jfi-inch  hlch-powcr  searchH^hls). 

TYPE  "C"  OPERATING  GEAR. 

Type  C  gearing  itself  is  almost  identical  with  that  of  type  B,  the  only 
difference  in  the  two  types  being  extended  handwheel  shafts.     This  is  used  on 


THE   SEABCHUGHT. 


123 


some  destroyers  and  on  any  other  ships  where  it  is  necessary  to  extend  the  shafts 
to  clear  the  searchUght  tower  or  other  obstruction.  The  general  plan  is  shown 
in  figure  134. 


WtlOKT    OF 

Jearchusht 


V/EI5HT    OF 
CotiTttOL 


Fig.  139.— Type  C  searchlight  operating  gear  ^attached  to  3e-inch  low-power  seareh|isiit , 


TYPE   "D"   OPERATING   GEAR. 


Type  D  operating  gear  consists  of  two  control  pedestals  used  in  pairs,  one 
right  hand  and  one  left  hand.  The  gearing  is  similar  to  that  of  types  B  and  C. 
Only  one  training  handwheel  shaft  extends  through  side  of  box.  The  shafts 
to  hght  are  concentric.  Figure  134  shows  the  general  arrangement.  This  type 
of  gearing  is  used  where  two  searchlights  are  mounted  close  together  on  a  tower 
or  on  twin  towers. 


126 


THB   BBASCHUOHT. 


S"Z?.- 


Fio.  iw.-OenermI  Electric  Co.s  type  of  searchUjht  operating  ge«r  (attached  to  Beck  36-incb  Usb-power saarcbUght J. 


THE    SEABCHLIGHT.  127 

TYPE  "E"  OPERATING  GEAR. 

Type  E  operating  gear  has  very  recently  been  designed  for  use  on  certain 
new  destroyers.     The  diagram  is  self-explanatory. 

"G.  E."   TYPE  OPERATING   GEAR. 

The  General  Electric  Co.'s  type  of  operating  gear  is  somewhat  similar  to 
type  B  gear,  except  that  only  two  handwheels  are  employed,  one  controlling 
elevation  on  one  side  of  pedestal  controUing  elevation,  and  one  controlling 
train  on  the  other  side  controlling  train.  Eight  of  these  operating  gear  sets  are 
used  on  the  Pennsylvania,  and  have  given  very  satisfactory  service.  Figure  134 
shows  general  arrangement. 

T\TES  OF  OPERATING  GEAR,  DISTANT  ELECTRICAL. 

There  are  two  fairlj-  satisfactory  types  of  distant  electric  control  in  use, 
the  Sperry  and  the  General  Electric ,  neither  of  which  is  on  the  follow-up  principle, 
but  operate  as  long  as  the  controller  is  on  the  "on"  position.  ITie  motion  is  in 
all  cases  transmitted  by  worms  and  worm  wheels  and  spur  or  bevel  gears. 

REMOTE      ELECTRICAL      OPERATING      GEAR     SYSTEM     FOR     SG-INCH     SEAKCHLIOHT. 

SPERRY   TYPE. 

The  Sperry  remote  control  system  is  imique  in  that  it  contains  no  moving 
parts  except  the  two  motors  which  serve  to  train  and  elevate  the  light.  Tlie 
entire  mechanism  is  inclosed  in  the  base  of  the  light,  protecting  all  parts  from 
the  weather.  Access  may  quickly  and  easily  be  had  to  each  and  eveiy  part  of 
the  system  by  removing  a  handhole  cover.  The  construction  is  rugged,  so  that 
the  system  vnR  stand  rough  usuage  without  getting  out  of  order.  It  will 
operate  successfully  under  all  ordinary  conditions. 

The  purpose  of  the  system,  to  find  the  target  and  keep  it  illuminated  from 
any  point  within  500  feet  of  the  'light  itself,  is  accomplished  by  a  reversible, 
variable  speed  motor  control  system.  There  are  two  motors,  one  to  rotate  the 
light  in  its  azimuth  and  the  other  to  rotate  it  in  elevation.  The  location  of 
the  working  parts  of  the  training  system  is  on  the  lower  half  of  the  base,  and  the 
elevating  motor  is  on  the  upper  half.  Tlie  training  motor  is  geared  to  the 
vertical  axis  of  the  light  by  means  of  a  worm  and  set  of  gears,  which  are  shown 
in  the  cut.  The  motor  can  be  disconnected  from  the  drum  by  means  of  a  clutch 
which  engages  or  disengages  one  pair  of  the  gears  in  the  train.  When  the  clutch 
is  out,  the  light  must  be  trained  by  hand ;  when  it  is  in,  the  light  is  trained  by  the 
remote  control  system. 

The  elevating  motor  is  moimted  on  the  rotating  part  of  the  base.  It  is 
geared  to  a  shaft  that  runs  up  along  one  of  the  trunnion  arms  through  a  worm 
and  gear  train,  which  is  shown  in  the  cut  (fig.  141).  This  shaft  is  geared  to  the 
elevating  rack  on  the  side  of  tl:e  drum.  A  clutch  is  provided  at  the  standard 
so  that  the  gear  can  be  made  to  engage  or  disengage  the  rack.  Thus  the  light 
can  be  elevated  either  by  hand  or  by  the  motor.  Since  this  motor  is  moimted 
on  the  rotating  part  of  the  base,  current  for  its  armature  and  field  is  led  to  it 
through  three  slip  rings,  shown  in  figirre  141.  The  brushes  which  ride  on  these 
rings  can  be  seen  on  the  upper  half  of  the  base.     The  two  wide  slip  rings  shown 


128  THE   SEAECHLIGHT. 

carry  the  current  for  the  arc.  The  speed  and  direction  of  the  motors  is  varied 
by  the  two  control  boxes  shown  in  the  cut.  One  of  tlicsc  regulates  the  eleva- 
tion, and  the  other  the  training  of  the  light.  It  is  seen  that  the  axes  of  the 
controlling  wheels  correspond  to  that  axis  of  rotation  of  the  light  which  it  con- 
trols; also  that  the  direction  of  rotation  of  the  controller  wheel  indicates  the 
direction  of  rotation  of  the  light.  This,  coupled  with  the  fact  that  the  con- 
trollere  can  be  so  placed  that  the  pair  may  be  operated  satisfactorily  either  by 
one  or  two  men,  as  the  occasion  calls  for,  is  one  of  the  advantages  of  this  S3'stem. 
Each  of  these  control  boxes  contains  a  multiple  point  switch.  The  points  on 
these  switches  are  connected  to  taps  on  the  potentiometer,  located  on  the  base 
of  the  light.  The  potentiometer  is  connected  across  the  120-volt  line  abend  of 
the  arc  rheostat,  so  that  the  potentiometer  voltage  is  constantly  120.  The 
simplicity  of  the  system  is  due  to  the  use  of  potentiometer  control  of  the 
motors.     It  operates  as  follows: 

The  field  of  each  motor  is  connected  across  one-half  of  the  potentiometer 
which  makes  the  field  constant  in  magnitude  and  direction.  One  side  of  each 
armature  is  connected  to  the  middle  or  neutral  point  of  the  potentiometer. 
The  other  side  of  the  training  motor  is  connected  to  the  switch  blade  in  the 
training  control  box,  and  the  other  side  of  the  elevating  motor  is  connected 
to  the  blade  in  the  elevating  controller.  The  connections  are  plainly  shown  on 
the  accompanying  wiring  diagram  (figure  143). 

Consider  first  the  training  motor.  If  the  switch  is  on  the  middle  point 
of  the  controller,  the  motor  is  short-circuited,  has  no  voltage  across  it,  and 
hence  will  not  rotate.  If  the  controller  is  moved  one  point  to  the  left, 
then  the  motor  armature  is  connected  across  a  few  turns  of  the  potentiometer. 
There  will  then  be  a  small  voltage  across  the  armature,  causing  it  to  revolve 
slowly.  If  the  controller  is  moved  farther  from  point  to  point,  more  and 
more  turns  are  included  in  the  armature  circuit,  causing  the  voltage  to  rise 
and  its  speed  to  increase.  When  the  last  point  is  reached,  the  annature  has  the 
maximum  voltage  across  it,  and  the  motor  is  ininning  at  maximum  speed.  If 
the  controller  handle  is  moved  in  the  other  direction  from  the  neutral  point, 
the  armature  polarity  is  reversed.  Since  the  polarity  of  the  field  remains 
unchanged,  the  motor  will  reverse  its  direction  and  increase  its  speed  as  the 
controller  is  moved  farther  and  farther  from  the  neutral  position.  When  it 
is  on  the  middle  point,  which  is  its  nonnal  position,  it  being  held  there  by 
springs,  the  armature  is  short-circuited,  which  applies  a  large  braking  efi'ect 
to  the  motor  and  causes  it  to  stop  quickly.  In  fact  the  drum  can  be  brought 
to  rest  from  full  speed  in  any  direction  in  less  than  2°  of  arc. 

A  glance  at  the  wiring  diagram  wiU  show  the  extreme  flcxibihty  of  the 
system.  On  the  present  type  of  this  control  there  are  17  taps  on  the  poten- 
tiometer, giving  8  different  speeds  in  either  direction,  varying  from  6°  to  360° 
of  arc  per  minute.  Both  motors  will  run  at  full  speed  in  either  direction,  and 
changing  the  speed  of  one  motor  when  the  other  is  running  will  not  affect  the 
speed  of  the  other  for  more  than  one-half  to  one  second. 

The  potentiometer  is  of  such  resistance  that  it  draws  about  four  amperes 
from  the  line  continuously,  but  can  safely  carry  considerably  more  than  this. 
Thus  either  or  both  motors  may  draw  sufficient  current  to  provide  enough  start- 
ing torque  to  bring  the  drum  from  rest  up  to  speed  in  less  than  5°  of  arc. 


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FIG.    I43.-SPERRY    DISTANT    ELECTRICAL  CONTROL   FOR   SEARCHLIGHTS   WIRING    DIAGRAM 

66438—18 9 


FIG,      U4      SPERRf      DISTAtlT      ELECTRICAL    CONTROL    FOR     SEARCHLIGHT     CONTROLLERS. 

BOXES    OPEN. 


FIG.    145. 


SPERRY      DISTANT      ELECTRIC     CONTROL     FOR     SEARCHLIGHT     CONTROLLERS. 
CABLES,    PLUGS,    AND    JUNCTION     BOX, 


FIG.     146.— SPERRY     DISTANT     ELECTRICAL    CONTROL    FOR    SEARCHLIGHT     CONTROLLERS. 

BOXES    CLOSED. 


THE   SEAKCHLIGHT. 


129 


This  system  provides  a  method  of  following  up  the  target  smoothly  and 
continuously,  not  in  the  jerky  manner  which  was  formerly  necessary.  The  range 
of  speeds  at  which  the  drum  can  be  rotated  is  wide  enough  to  satisfy  all  con- 
ditions met  with  in  practice.  Moreover,  the  system  is  by  far  the  simplest 
which  has  yet  been  devised,  in  addition  to  which  it  is  of  such  rugged  con- 
struction that  it  will  not  get  out  of  order  except  under  extreme  conditions. 
If  it  should  break  down,  repairs  can  be  made  with  extreme  faciUty  as  every 
part  of  the  system  is  easily  accessible. 

The  system  of  remote  electrical  operating  gear  supplied  by  the  General 
Electric  Co.,  is  very  similar  to  the  Sperry  system. 

THE    GKNEKAL    ELECTRIC   CO.    SYSTEM. 

The  system  of  training  these  projectors  in  altitude  and  azimuth  diflfers 
from  previous  methods  employed,  a  synchronous  training  arrangement  being 
provided  between  the  controller  and  the  projector. 


Fro.  147.— Assembly  of  horizontal  training  mechanism. 

On  the  controller,  figure  149,  there  are  two  separate  handwheels,  one  for 
each  plane  of  control.  These  handwheels  rotate  by  means  of  shafts  and  simple 
commutating  devices,  which  commutate  the  direct  current  to  currents  having 
three-phase  relation.  This  causes  to  rotate,  in  the  base  and  on  the  turntable 
of  the  projector,  pilot  motors  which  have  the  same  direction,  speed,  and  relative 
magnitude  of  rotation  as  that  of  the  commutating  devices  or  the  handwheels 
rotating  the  same. 

Referring  to  figure  147,  it  will  be  seen  that  the  pilot  motor  (D)  consists 
of  6-pole  pieces,  on  each  of  which  are  moimted  two  stationary  coils  which  will  be 
referred  to  as  the  armature  coils.  These  pole  pieces  are  arranged  on  the  cir- 
ciimference  of  a  circle,  inside  of  which  is  placed  a  movable  field  excited  by  two 
stationary  coUs  connected  in  series  across  the  training  circuit,  as  shown  in 
figure  151. 


130  THE   SEARCHLIGHT. 

Tho  armature  coils  on  each  pole  piece  aro  connected  in  series,  the  coils 
on  tho  different  pole  pieces  being  so  interconnected  as  to  leave  three  leads 
which  run  back  to  the  controller. 

The  field  of  this  motor  is  so  constructed  as  to  take  up  12  definite  equidis- 
tant positions  for  one  complete  revolution;  each  position  depending  on  the 
combination  of  current  through  leads  3,  which  run  back  to  the  controller.  It 
will  thus  be  seen  that  diflereut  current  combinations  through  tho  pilot  motor, 
caused  by  rotating  the  handwheel  of  tho  cohtrollcr,  will  cause  the  field  of  the 
pilot  motor  to  rotate. 

Rotating  tho  horizontal  training  handwheel  on  the  controller  through  half  a 
revolution  causes  the  revolving  field  of  the  pilot  motor  (D),  fig.  147,  in  tho 
projector  to  rotate  one-fourth  of  a  revolution  or  90°.  The  rotation  of  this  motor 
field  causes  the  cam  cjdinder  (E)  to  rotate,  for  example,  through  l.'j°,  by  moans 
of  the  spiir  gears  (F),  (G),  (H),  and  (I),  and  the  bevel  box  gearing  (J),  (K,) 
and  (Tj)  ;  (K)  not  being  visible  in  the  upper  view  on  account  of  its  not  occurring 
on  the  section,  but  engaging  with  (J)  and  (L). 

The  operation  of  the  cam  cylinder  (E)  operates  the  contact  fingers  (M), 
connecting  tho  training  motor  (N)  to  tlio  circuit  for  tho  proper  direc- 
tion of  rotation.  Tho  projector  then  begins  to  rotate  by  moans  of  the 
worm  (O)  attached  to  the  motor,  the  worm  gear  (P)  and  spur  gearing  (K)  and 
(S)  which  is  connected  by  means  of  the  spur  gear  (T)  to  tho  main  training  gear 
rinf  which  is  fastened  to  the  turntable.  Connected  to  the  shaft  (U)  is  the 
bevel  fear  (V)  whicU,  through  tho  diff'erential  gears  (L)  and  (K) ,  also  drives  the 
cam  cylinder  (E),  but  in  a  direction  opposite  to  the  rotation  induced  by  the 
pilot  motor,  so  that  wlien  tlae  turntable  has  rotated  through  1°  it  will  have 
turned  (E)  back  to  its  off  position,  stopping  the  training  motor. 

To  sum  up,  the  cam  cylinder  (E)  has  a  motion  equivalent  to  the  alge- 
braic sum  of  the  motions  derived  from  the  pilot  motor  and  tho  training  shaft 
(U)  and  is  always  equal  to  zero.  The  explanation  of  these  movements  has 
been  made  as  if  they  occurred  separately;  but,  as  a  matter  of  fact,  as  soon  as 
the  cam  cylinder  (E)  is  rotated  by  the  rotation  of  tho  pilot  motor,  the  pro- 
jector begins  to  revolve  and  in  so  doing  tends  to  rotate  the  cam  cyhndor  back 
to  its  original  off  position.  As  long  as  the  controller  handwheel  is  rotated 
the  projector  will  continue  to  rotate. 

From  this  description  it  will  be  gathered  that  a  half  turn  of  the  controller 
handle  corresponds  to  1°  movement  of  the  projector  beam,  and  that  if  tlie 
controller  handle  bo  turned  through  10  one-half  revolutions  the  beam  will 
travel  through  10°  at  tho  same  relative  speed  of  rotation  as  the  handle.  It 
will  thus  bo  seen  that  a  slow  movement  of  tho  controller  handle  results  in  a  slow 
movement  of  the  beam,  and  a  rapid  movement  of  the  controller  handle  will 
produce  a  rapid  movement  of  tho  beam.  For  slow  movements  of  tho  con- 
troller handle  the  training  motor  (N)  is  connected  to  the  circuit  through  re- 
sistances; for  greater  speed  the  resistance  are  short  circuited  by  one  of  tho 
contact  finders  (M)  for  faster  speeds  of  training.  If  the  speed  of  rotation  of 
the  handwheel  is  relatively  faster  than  the  rotation  of  the  turntable,  there  will 
be  a  sU<^ht  lag  in  tho  beam  but  the  projector  will  catch  up  and  stop  at  the 

proper  angle. 

The  vertical  training  gear,  shown  on  figure  148,  is  the  same  as  the  hori- 
zontal except  for  the  difference  in  the  mechanical  connection  between  the 
training  motor  and  the  projector  barrel. 


FIG.   143.—ASSEMBLY   OF   VERTICAL   TRAINING    MECHANISM. 


FIG.    149. —PARTS   OF   THE   FORM    N-I    PROJECTOR   CONTROLLER. 


A=  Vertical  adjust iiif;  Ihumbscrew. 

B=  Horizontal  adjust  iii^'  t  Immbscrew. 

C=SiL''it  h:ir  o[)pr;iliii,Lr  scri'W. 

D^  I  Im  I  niii  il  h  ;iiTiin^  liandwlieel. 

■£=-  \  el  1  !'■  >|  I  i.iining  luuidwheel. 

F=  J-iRkiu^  ii»d  armature  spring. 

G  =  Locking;  coil  armature. 

H=  Vertical  control  contact  drum. 

1=  Sight  bar. 

J=  Sight  bar  standard. 

K=  Top  plate. 

L=  Frame. 

M=  Bottom  plate. 

N=  Receptacle  shell. 


<)=  Receptacle  contacts. 

P=  Locking  coil. 

0=Horizontal  control  contact  drum. 

R=  Frame  for  horisontal  control  con- 
tact drum. 

S=Contact  finger  for  vertical  control 
contact  drum. 

T=Stop  plate  for  vertical  control 
handwlioel  worm  gear. 

U=\Vorm  gear  for  vertical  control 
handwheel. 

V=  Bevel  gear  for  sight  bar  operatiJig 
screw. 

W=-  Worm  gear  for  horizontal  control . 


X=  Worm  for  horizontal  control  hand- 
wliee. . 

Y=^Tvnob  for  horizontal  training  hand- 
wheel  . 

Z=Knob  for  vertical  training  hand- 
wheel. 

Aa=Cap  for  cable  receptacle. 

Ba=  Chain  for  caltle  receptacle  cap. 

Ca=  Contact  plunger. 

Da=  Shaft  for  vertical  control  hand- 
wheel. 

Ea=Oear  for  sight  bar  operating  screw. 

Fa=Collar  for  vertical  control  hand- 
shaft. 


In  ordering,  give  niinie  of  pari .  reference  letter,  and  figure  number. 


THE   SEARCHLIGHT. 
THE  CONTROLLER. 


1^1 


The  controller  is  provided  with  a  sight  bar  which  moves  synchronously 
with  the  projector  beam;  this  is  shown  in  figures  149  and  150.  The  operating 
handwheels  which  train  the  projector  are  geared  to  the  sight  bar  so  that  the 


movements  of  the  sight  bar  in  altitude  and  azimuth  correspond  to  the  move- 
ments of  the  projector  beam.  It  will  be  seen  that  if  the  controller  sight  bar 
and  the  projector  beam  are  in  orientation,  the  projector  will  be  pointed  at  the 
target,  if  the  Hne  of  sight  of  the  sight  bar  is  on  the  target. 


182 


THE   SEAHCHUQHT. 


A  convenient  method  of  orienting  is  to  bring  the  projector  beam  and  the 
line  of  sight  of  the  sight  bar  together  on  a  common  object  at  some  distance, 
after  which  the  projector  is  clamped  to  the  electric  control.  A  clutch  is  pro- 
vided for  this  purpose  on  the  handwheels,  and  any  slight  variation  in  aligiunent 
may  be  corrected  by  adjustments  on  the  controller,  the  thumbscrews  (A)  and 
(B)  (fig.  149).  being  ])rovided  for  this  purpose. 

Referring  to  figure  149,  the  locking  coil  (P)  locks  the  horizontal  and 
vertical  handwheels  when  the  voltage  on  the  training  motors  fails  or  is  cut  off, 
thus  preventing  the  sight  bar  from  becoming  out  of  orientation  with  the  pro- 
jector. Another  function  of  this  coil  is  to  lock  the  handwheels  in  case  the 
speed  of  rotation  of  the  controller  handwheels  is  greater  than  the  relative 
speed  of  the  beam,  thus  allowing  the  beam  to  catch  up  and  preserv^ing  the 
orientation.  In  this  case  the  operation  of  the  coil  is  effected  by  opening  its 
circuit  through  one  of  the  cam  fingers  (M)  operated  by  the  pilot  motor. 


^22li 


Fig.  150.— Assembly  of  Form  N  projector  oontroUer. 

Electric  o])erating  gears  are  used  to  only  a  hmited  e.xtent  aboard  ship 
because,  though  they  are  rugged  and  operate  successfully  at  fii-st,  they  deterior- 
ate rapidly.  They  are  necessarily  more  complicated  than  mechanical  operating 
gears;  repairs  are  more  difficult  to  make  and  require  a  higher  grade  of  work- 
manship than  is  usuallj-  obtainable  on  board  ships  of  the  Navy.  Mechanical 
operating  gears  are  preferred  because  they  are  simpler,  less  liable  to  require 
repairs,  and  more  easily  repaired.  Moreover,  with  mechanical  gear  systems, 
the  operator  feels  that  he  is  in  tangible  connection  with  the  searchlight  and 
is  more  conscious  of  absolute  control  of  the  movements  of  the  light. 


CHAPTER  11. 
TABLES  OF  GENERAL  DATA  ON  SEARCHLIGHTS  AND  BLINKERS. 


INDEX   TO   TABLES. 

Table. 

1.  Signaling  distance  (miles)  of  searchlights  and  blinkers. 

2.  Target  illuminating  distance  (yards). 

3.  Searchlight  currents,  voltages,  and  wattages. 

4.  Depression  angles  to  bring  searchlight  beam  on  targets  (degrees). 

5.  Deflection  of  beam  (feet)  at  various  ranges,  corresponding  to  training  searchlight  through 

an  angle  of  1  degree. 

6.  Beam-spread  angles  (degrees). 

7.  Beam  diameters  (feet)  at  various  ranges. 

8.  Weights  of  searchlights,  rheostats,  etc.  (pounds). 

TABLES  OF  GENERAL  SEARCHUGHT  DATA. 

Following  are  tables  which  ^re  of  some  interest  in  connection  with  search- 
light and  signal  equipment: 

TABLE  1. 
SIGNALING   DISTANCES    (iN    MILES)    OF   SEARCHLIGHTS   AND    BLINKERS. 

The  distances  given  in  this  table  are  the  average  values  of  signaling  dis- 
tances, the  average  being  computed  from  a  number  of  reports  on  distances  at 
which  signals  could  be  read  in  clear  weather. 

Signaling  distances  {in  miles)  of  searchlights  and  blinkers. 


36-inch  low-power 
searchlight. 

30-inch  low-po^er 
searchlight. 

12-inch  arc  signal 
searchlight. 

Day. 

Night. 

Day. 

Night. 

Day. 

Night. 

15 

30-35 

12 

30 

9 

16 

12-inch  incandescent  sig- 
nal searchlight. 

Yardarm  blinker. 

Portable  tube  blinker. 

Day. 

Night. 

Day. 

Night. 

Day. 

Night. 

2.5-3 

7-10 

0 

1 

5          '          0 

2.5-3 

No  data  is  available  on  the  distance  at  which  signals  by  high-power 
searchlight  may  be  read,  but  as  the  beam  is  so  much  more  powerful  than  the 
beam  of  a  low-power  searchlight  the  distances  are  probably  very  much  greater. 


133 


134 


THE   BEABCHUGHT. 


It  is  expoctod  that  the  range  and  speed  of  incandescent  signal  searchhghts 
and  of  bUnkers  will  be  increased  considerably  by  using  high-speed,  concen- 
trated filament  lamps. 

T.\ROET-lLLUMlNATINQ    DISTANCES    (yARDS). 

I 

The  information  about  ranges  at  which  targets  can  bo  illuminated  is  very 
meager  owng  to  the  fact  that  but  few  tests  have  been  made  idong  this  line. 
The  vtUues  given  are  appro.xiiuato  and  are  for  clear  weather. 

TABLE  2. 

Target-illuminalion  ranges  (yaMi). 


I 


Range-finder        Target  plain 
readings.  (nated  eyeV 


Target  plain       ,,ig-ihiV(,^i-„o,,. 
ibinorularsl.  ,.,„!, 


Target  just 

'ble  (bii 

ularsK 


36-inch      low-power 

searchhght    j  2,000-2,500  3.  500  4,  000  6,  000 

36-inch     high-power 

searclilight . 4,  500  6,  000  8,  000      10.000-12,000 

24-inch     high-power 

searchhght 2,500  |  4,000-4,500  |  5,500-6,000  8,000 

i  I ' 


TABLE  3. 


SEARCHLIGUT    CURRENTS,    VOLTAGES,    AND    WATTAOE8. 

The  values  in  Table  3  are  given  as  an  aid  in  selecting  searchlight  material 
suitable  to  the  generator  capacity  available. 

Searchlight  currenU.  voltage*,  and  wattages. 


•    ' 

Arc  volt- 
age 

(volts>. 

.Miuimum 
supply 
vo  tage 
recom- 
mended.* 

Average  power  (kilowatts). 

Sizeofeearchlighl.           (f^,",",^) 

1 

In  arc. 

Consumed 

in  rheo- 

Btat.t 

Total. 

9-inch  arc. 10 

12-inch  arc 20 

18-inch 35 

24-inch  low  power...            50 
30-inch  low  power...            80 
36-inch  low  power...          120 
24-inch  high  power.  .            75 
30-inch  high  power.  .          120 
36-inch  high  power. .          150 

45 

45 

50-54 

50-54 

55-59 

58-62 

45 

72 

75 

70 

70 

80 

80 

90 

100 

70 

110 

110 

0.45 

.9 
1.82 
2.6 
4.54 
7.2 
3.  375 
8.64 
11.25 

0.25 
.5 
.98 
1.4 
2.46 
4.8 
1.875 
4.56 
5.25 

0.7 

1.4 

2.8 

4.0 

7.0 

12.0 

5.25 

13.20 

16.50 

•  To  obtain  the  proper  balance  for  steady  burning  the  supply  voltaEe  should  be  not  less  than  1.5  times  arc  voltage 
t  Based  on  a  drop  across  rheostat  equal  to  difference  between  "  Minimum  Supply  Voltace  Recommended     and 
"Arc  Voltage." 


THE   SEABCHLIGHT.  135 

TABLE  4. 
DEPRESSION    ANGLES    TO    BRING    SEARCHLIGHT    BEAM    ON    TARGETS. 

The  following  table  shows  angle  of  depression  of  searchlight  required  to 
bring  the  center  of  the  beam  on  the  water  line  of  the  target  at  different  ranges 
from  different  searchlight  mounting  heights  measured  from  the  water  line  to 
the  searchlight  trunnions. 

'.  Height  of  searchlight  trunnions  above  water  line  (feet). 


Range  (yards).  |         40 


45 -f- 


50 


55 


60 


65 


68'  5'' 


Depression  angles. 


O         /  ft        O         ! 


2,400. 
4,000. 
8,000. 


0  19     6 

0  11  28 
0     5  44 


//      'O  /  ff        O  f  //        0  /  f  f      \      O         t  tl 


0  21  29  10  23  16  :0  26  16 
0  12  53  0  14  19  0  15  45 
0     6  27  :0     7   10    0     7  53 


0  28  39  lO  31  2  I  0  32  40 
0  17  11  lO  18  37  I  0  19  36 
0     8  36   0     9  19  :  0     9  4S 


The  trunnion  of  the  searchlight  on  the  forward  mast  of  the  OMahoma  is  68 
feet  5  inches  above  water  hne,  therefore  the  angle  of  depression  required  to 
put  the  center  line  of  beam  on  the  water  line  of  target  at  8,000  yards  range 
is  0°  9'  48". 

Note.— The  curvature  of  the  earth  was  not  considered  in  calculating  above  table.  The 
difference  would  be  slight  at  the  shorter  ranges  and  not  important  at  the  longer  range  of  8.000 
yards. 

TABLE  5. 

Deflection  of  beam  at  various  ranges  corresponding  to  training  searchlight  through  an  angle  of  one 

degree. 


Range  (yards). 


'  I  I 

2,000     '     4,000     I     6,000     '     8,000 

i- ^1 


Training  searchlight  1 
degree  moves  beam 
..feet. J       104  208         312  416 


10.000 


12,000 


520  i       624 


TABLE  6. 

Beam -spread  angles  of  high-power  searchlights. 


Size  of  light. 

Beam-spread  air- 
cooled  searchlights. 

Beam-spread  Beck 
searchlights. 

60  inches 

36  inches 

30  inches    .    .    . 

1°  15' 
2°    0' 

None  made. 
2°  20' 
2°  20' 

24  inches 

2°    0' 

No  data  is  available  on  the  beam  spread  of  low-power  searchlights. 


136 


THE   gEAHCHLIOHT. 


TABLE  7. 
BEAM    DIAMETERS    AT    VARIOUS   RANGES — HIOH-POWER    SEARCHLIGHTS. 

This  table  shows  the  importance  of  having  accurate  mirrors  and  of  keeping 
the  positive  carbon  crater  exactly  in  the  focus  of  the  mirror,  inasmuch  as 
the  target  illumination  in  foot  candles  varies  inversely  as  the  square  of  the 
diameter  of  the  beam  at  that  point,  if  atmospheric  absorption  be  neglected. 
Atmospheric  absorption  is  approximately  10  per  cent  for  1,000-yards  range 
i.  e.,  only  90  per  cent  of  the  total  light  in  the  beam  outside  of  the  front  door 
strips. 

If  the  beam-spread  angle  could  be  reduced  to  one-half  its  original  angle  the 
illumination  on  the  target  would  be  four  times  its  original  value,  hence  the  neces- 
sity of  keeping  the  beam  as  concentrated  as  possible.  The  beam-spread  angles 
increase  very  rapidly  as  crater  of  positive  carbon  is  moved  out  of  focus  of  the 
mirror. 

BEAM    DIAMETERS    .\T    VARIOUS    RANGES HIGH-POWER    SEARCHLIGHTS. 

60-inch  air-cooled  high-power  searchlight — Beam  spread  1°  15'. 


Range  (yards) 

2,000 

4,000 

6,000 

8,000 

10,  000 

12,  000 

Beam  diameter  (feet)..        131 

262 

393 

524 

655 

786 

36  and  24  inch  air 

-cooled  high-power  searchlight — Beam  spread  2°  V . 

Range  (yards) 

Beam  diameter  (feet) . . 

2,000 

4,000 

6,000 

8,000 

10,  000 

12,000     1 
1, 260     ' 

210 

420 

630 

840 

1,050 

so  and  36  inch  Beck  {alcohol  "cooled*')  high-power  searchlight — Beam  spread  2°  20". 


Range  (yards) 

2,000 

4,000 

6,000 

8,000 

10,  000 

12, 000 

Beam  diameter  (feet) . . 

251 

502 

753 

1,004 

1,255 

1,506 

TABLE  8. 

WEIGHTS    OF    SEARCHLIGHTS,    RHEOSTATS,    ETC. 

HIGH-POWER  SEARCHLIOHTS. 

36-INCH    BECK    (GENERAL    ELECTBIC    CO.)    HIGH    POWER. 

Pounds. 

Searchhght 1,670 

Rheostat  (125-volt  circuit) .- 490 

30-INCH    BECK    (general    ELECTRIC   CO.)    HIGH    POWER 

Searchhght 1,490 

Rheostat  (125-volt  CHCuit) 429 

24-INCH   GENERAL   ELECTRIC  CO.   AIB-COOLED    HIGH   POWER. 

Searchhght 1,045 

Rheostat  (125-volt  circuit) 360 


TBTE  SEABOHLIOHT.  137 

36-INCH   8FERBT  HIOH   FOWBB. 

Ponnds 

Searchlight 1 ,  628 

Rheostat  (125-volt  circuit) 210 

36-INCH   8PEBRT-OENERAI.   ELECTHIC   HIGH-PO WEB  CONVERTED. 

General  Electric  Co.,  drum  before  fitting 1,  100 

Conversion  parts: 

Sp«ny  high-power  lamp  for  conversion 70 

All  conversion  parts 385 

36-inch  Sperry-General  Electric  converted  searchlight  1 1 ,  485 

Eheostat  (125-volt  circuit) 210 

24-INCH    3PERRY   HIOH   FOWKK. 

Searchlight 975 

Rheostat  (125-volt  circuit) 120 

24-INCH  ABMA   HIOH   POWER. 

Searchhght 791 

Lamp 70 

Rheostat  (125-volt  circuit) 125 

Rheostat  (80-volt  circuit) 120 

LOW-POWER  SEARCHLIGHTS. 
36-INCH   GENERAL   ELECTRIC,    >fAVT   STANDARD,    LOW   POWER. 

Searchlight _ 1,  800 

Rheostat  (125-volt  circuit) 315 

Signal  shutter 72 

125  pairs  carbons ._  138 

Spare  lamp  in  box 59 

30-INCH   GENERAL   ELECTRIC,    NAVY  STANDARD,    LOW   POWER. 

Searciilight 910 

Rheostat  (80-volt  circuit) 225 

24-INCH   GENERAL    ELECTRIC,    COHMBRCLAL,    LOW   POWER. 

Searchhght. 725 

Rheostat  (125-volt  circuit) 135 

18-INCH   GB.VERAL    ELECTRIC,    COMMERCIAL,    LOW   POWER. 

Searchhght. 230 

Rheostat  (125-volt  circuit) 125 

12-INCH   GENERAL   ELECTRIC,    NAVY   STANDARD,    ARC   SIGNAL. 

Searchlight 93.5 

Rheostat  (r25-volt  circuit) 96.  0 

9-INCH   GENERAL    ELECTRIC,    NAVY   STANDARD,    SUBMARINE   ABC. 

Searchhght 83 

Rheostat  (110-volt  circuit) ._  60 


138  THE   SEAHCHLIGHT. 

12-IKCH   CARLISLE    i    FINCH,    NAVV   STANDARD,    ARC   BIONAL. 

Poonds. 

Searchlight -  - - - 110 

Rheostat  (r25-volt  circuit),  approximately 95 

12-INCH   INCANDESCENT  SIGNAL   SEARCHLIGHT. 

Searchlight • - 30-45 

(Weights  vary  for  different  manufacturers'  lights.) 


CHAPTER   12. 
CARBONS  FOR  SEARCHLIGHTS. 


CARBONS  FOR  SEARCHIJGHTS. 

Searchlight  carbons  are  of  great  importance  in  the  efficient  operation  of 
any  arc  searchlight.  They  must  be  so  made  as  to  feed  smoothly. burn  evenly, 
not  crack  or  flake,  and  not  sputter.  Dampness  is  injurious  to  all  carbons,  in 
that  it  causes  them  to  sputter  and  burn  unevenly  and  with  a  flickering  light. 
This  is  particularly  true  in  the  case  of  high-power  searchlight  carbons  which 
have  a  special  core.  Not  only  does  dampness  cause  flickering  and  sputtering, 
but  it  may  also  loosen  the  core  and  cause  parts  of  it  to  break  oft,  destroying 
the  shape  of  the  crater  and  seriously  impairing  the  illuminating  power  of  the 
searclalight.  It  is  of  prime  importance  to  keep  in  mind  the  fact  that  carhons  are 
■porous  and  absorb  moisture  from  the  atmosphere.  They  are  more  absorbent  of 
salt  water  than  of  fresh  water.  It  is  imperative  therefore  that  the  containers 
of  carbons  be  kept  tightly  closed  and  sealed,  if  best  results  are  to  be  obtained. 

Tlie  chief  difference  between  the  illumination  given  by  "low-power" 
carbon  arcs  and  "high-power"  cored  carbon  arcs,  is  due  to  the  higher  intrinsic 
brilliancy  of  the  surface  of  the  high-power  positive  carbon  crater  and  to  the 
smaller  crater  diameter.  The  high  intrinsic  brilliancy  is  caused  by  the  higher 
current  density  in  the  arc  and  the  higher  temperature  produced  thereby,  and 
by  the  mass  of  highly  incandescent  gases  in  the  positive  crater  produced  by  the 
volatilization  of  the  salts  composing  the  positive  and  negative  cores. 

The  following  table  taken  from  an  article  printed  in  the  Aerial  Age,  Sep- 
tember 4,  1916,  on  the  Sperry  air-cooled,  high-power  searchlight  shows  some- 
what the  improvement  made  over  the  old  low-power  searchlight  illuminating 
power  in  brilliancy. 

Tlie  figures  are  for  specific  brilliancies  in  candlepower  per  square  millimeter. 

(1)  Candleflame 0.01 

(2)  Acetylene  flame - .       0.  08 

(3)  Carbon-filament  lamp  . 1 .  00 

(4)  Ordinary  tungsten  lamp 2.  0  to  4.  0 

(5)  Gas-fiUed  tungsten  lamp 10.  0  to  20.  0 

(6)  Tungsten  at  the  melting  point  (3,500°  C.) 72.  0 

(7)  Arc  flame,  ordinary  white  flame  arc 7.  0  to  20.  0 

(8)  Crater  of  carbon  arc 110.0  to  160.0 

(9)  Crater  of  Sperry  arc 550.  0  to  800.  0 

(10)  Sun  at  30  degrees  elevation 775.  0 

(11)  Sun  at  noon 930.  0 

Not  only  is  there  a  vast  increase  in  brOliancy  but  there  is  abo  a  great 
improvement  in  the  character  of  the  light.  The  low-power  searclilight  beam 
appears  foggy  and  yellow  when  compared  to  the  clear  bluish  beam  of  the  high- 

139 


140  THE   SEABCHUGHT. 

power  searchlight.     The  beam  is  a  pale  blue,  particularly  at  twilight  or  dawn, 
although  the  spectroscope  analysis  of  the  light  shows  it  to  be  of  a  greenish  hue. 

Spectrophotometer  analysis  of  the  beam  of  a  low-power  searchlight  shows  it 
to  have  its  greatest  intensity  at  a  wave  length  of  0.58  microns  (a  micron  =  0.001 
millimeter),  which  is  in  the  yellow  part  of  the  spectrum.  The  high-power 
hght  has  its  greatest  intensity  at  0.55  microns,  which  is  in  the  green  part  of  the 
spectrum.  Light  of  this  particular  wave  length  reflects  better  from  a  mirror 
than  hght  of  a  wave  length  of  0.58  micron,  and  has  a  greater  illuminating 
power  of  objects  of  gray,  blue,  black,  or  green  colors,  such  as  are  most  frequently 
met  with  at  sea;  i.  e.,  it  reflects  better  from  surfaces  of  those  colors.  Battle 
gray  Ls  no  protection  against  the  light  of  the  high-power  searclilight,  while  in 
the  light  of  a  low-power  searchliglit  it  shows  dull  and  dead. 

Specifications  for  liigh-power  carbons  must  be  based  on  spectrophotometer 
analysis  of  the  hght  given  off,  inasmuch  as  the  composition  of  the  cores  are 
knoA^Ti  only  to  the  manufacturers,  and  hence  can  not  be  specified. 

Specifications  for  searchhght  carbons  are  given  below.  It  will  be  noted 
that  Sperry  searchhght  negative  carbons  are  copper  coated,  while  the  other 
high-power  searchlight  carbons  are  not.  This  copper  coating  is  an  undesirable 
featme,  inasmuch  as  lumps  of  molten  copper  may  drop  on  the  mirror  and  cause 
breakage  when  operated  in  the  antiaircraft  position;  also,  the  coating  may 
melt  and  "spot-weld"  the  carbon  into  the  negative  head,  preventing  feeding. 
The  Sperry  lamp  negative  head  will  be  altered  in  construction  in  the  future  so 
that  imcoated  liigh-power  carbons  may  be  used,  thus  providing  a  standard 
carbon  for  all  liigh-power  searchhghts  of  the  same  size. 

Two  sets  of  specifications  are  given  for  low-power  searchhght  carbons,  as 
man^'  of  the  older  type  of  carbons  are  in  use  and  are  being  supphcd,  while 
improvements  have  necessitated  a  change  of  specifications  for  carbons  used 
in  later  low-power  lamps. 

17C5a. 
Superseded  by  17C5b. 
Navy  Department  Specifications. 

LOW-POWER  8EAECHLIGHT  CARBONS  FOB  USE  IN  THE  tTNirED  STATES  NAVT. 

June  1,  1917. 

General  specifications. 

1 .  General  Specifications  for  Inspection  of  Material,  issued  by  the  Navy 
Department,  in  effect  at  date  of  opening  of  bids,  shall  form  part  of  these 
specifications. 

Gteneral  description. 

2.  Carbons  shall  be  circular  in  cross  section,  uniform  in  diameter  for  the 
entire  length,  homogeneoiLs  in  texture,  and  free  from  all  flaws,  cracks,  or  im- 
purities which  may  cause  unsteady  burning.  The  carbons  covered  by  these 
specifications  are  of  two  classes,  known  as  the  3-to-2-ratio  and  the  1 -to- 1 -ratio 
carbons.  These  terms  refer  to  the  rate  of  burning  of  positive  with  reference 
to  negative. 

Dimensions,  current,  and  arc  voltage. 

3.  The  tables  following  give  the  general  dimensions,  current,  and  arc  volt- 
age of  the  two  types  of  searchhght  carbons. 


THE   SEAKCHLIGHT. 
(a)  JHmensions  for  the  l-to-1-ratio  carbons. 


141 


Bizeof 
search- 
light. 

Current 
amperes. 

Arc 
voltage. 

Dimensions  in  millimeters. 

Positive        Positive 
diameter.        length. 

1 

Negative 
diameter. 

Negative 
length. 

India. 
9 
12 
18 
24 
30 
36 

10 
20 
35 
50 
SO 
120 

48-51 
50-54 
50-54 
55-59 
oS-«2 

13 
16 
16 
19 
25 
28.  S 

120 
140 
180 
250 
250 
250 

I 

9 
10 

11.5 
13 

110 
130 
160 
230 

230 
230 

(6)  Dimensions  for  the  S-to-2-ratio  carbons. 


1 

^t  1  »'"p^'*^- 

1 

Arc 
voltage. 

Dimensions  in  inche-s. 

Positive 
diameter. 

Positive 
length. 

Negative  j    Negative 
diameter.        length. 

t 

India. 

9                  10 
12                  20 
18                  35 
24                  50 
30                   80 
1               36                110 
1                      1      • 

45 
45 
45 
45 
45 
60 

t 

1 

li 

6 

8i 
12 
12 
12 

i    r 

1                       " 

Negative  carbons. 

4.  (a)   For  1-to-l  ratio. 

The  negative  carbon  for  the  1-to-l-ratio  carbons  shall  consist  of  a  solid 
carbon,  heavily  copper  coated  over  its  entire  length.  It  shall  be  uniform  in 
diameter,  and  one  end  shall  be  tapered  to  a  point  at  an  angle  of  about  70  degrees. 
The  carbon  shall  be  hard,  homogeneous  in  texture,  thoroughly  baked,  and 
straight.  It  shall  be  free  from  any  imperfection  which  may  cause  the  arc  to 
hiss  or  fhcker.  The  dimensions  for  carbons  for  various  sizes  of  searchlights 
can  be  found  in  table  forming  part  of  these  specifications. 

(6)   For  S-to-2  ratio. 

The  negative  carbons  for  the  3-to-2-ratio  carbons  shall  consist  of  a  shell  and 
core,  the  shell  being  a  hard,  homogeneous  carbon,  and  the  core  shall  be  soft 
carbon.  The  negatives  for  the  36  and  30  inch  searchhghts  shall  be  copper 
coated  for  their  entire  length,  while  those  for  all  other  sizes  of  searchhghts 
shall  be  plain.  The  dimensions  of  carbons  for  various  sizes  of  searchlights  can 
be  found  under  table  forming  part  of  these  specifications. 

Positive  carbons. 

5.  The  positive  carbon  shall  consist  of  two  parts,  namely,  the  shell  and 
the  core. 

(a)   The  shell. 

The  shell  shall  be  homogeneous  in  texture,  free  from  injurious  imperfec- 
tions, thoroughly  baked,  and  one  end  slightly  tapered,  with  a  crater  formed. 

(6)   The  core. 

The  core  of  the  positive  carbon  shall  be  composed  of  a  hard  white  flame 
material,  of  uniform  circular  cross  section,  shall  run  evenly  in  the  center  of  the 
shell,  and  shall  be  so  fitted  in  the  shell  as  to  eliminate  any  spaces  between  it 
and  the  shell  which  may  tend  to  cause  flickering  of  the  arc.     The  structure  of 


142  THE   SEAECHLIQHT. 

the  core  shall  be  such  that  it  shall  not  crumble  or  loosen  from  the  shell  without 
the  actual  breaking  of  the  shell  from  the  core.  The  dimensions  for  various 
sizes  of  searchlijrhts  are  shown  under  a  table  formini;  part  of  these  specifications. 

Ratios  of  burning. 

6.  (a)  The  ratio  of  burning  of  the  carbons  known  as  the  1-to-l  ratio 
shall  be  1  part  by  length  and  by  weight  of  positive  to  1  part  by  length  and  by 
weight  of  negative. 

(b)  The  ratio  of  burning  of  the  carbons  known  as  the  3-to-2  ratio  shall  be 
3  parts  by  length  and  weight  of  positive  to  2  parts  by  length  and  weight  of 
negative. 

Performance  when  burning  under  normal  conditions. 

7.  The  carbons,  when  burning  under  normal  conditions,  shall  burn  without 
dickering  or  sputtering,  shall  not  crack  and  throw  off  chips,  and  shall  give  ofT 
a  small  quantity  of  ash.  The  liame  shall  not  l)e  excessive  and  the  composition 
of  the  flaming  material  shall  be  such  that  the  combustion  shall  be  complete, 
no  soot  being  formed  which  will  deposit  on  the  mirror  or  finders,  thus  impairing 
the  range  of  the  light. 

Minimum  candlepower. 

8.  The  following  table  gives  values  of  the  candlepower  of  tlie  arc,  l)urning 
under  normal  conditions,  which  will  be  considered  a  minimum  acceptable 
maximum  value,  for  the  carbons  for  different  sizes  of  searchlights. 


size  of 
searchlight. 

3-to-2  ratia 

1-to-l  ratio. 

1 

1     India. 

Canilf 

Candle- 

power. 

power. 

1               » 

900 

I, MO    , 

12 

2,200 

3,.tOO 

18 

.■i.Oflfl 

7,500 

24 

9,000 

11,500 

30 

15,000 

20,000 

36 

1 

25,000 

.•12,000 

General  characteristics  of  light  from  arc. 

9.   (a)   Color  of  crater  luild. 

The  light  from  the  arc  formed  on  these  carbons  shall  be  decidedly  blue  in 
color,  and  upon  spectnim  anah-sis  shall  show  at  least  5  per  cent  of  the  total 
energy  below  wave  length  0.002  micron,  30  per  cent  of  total  energy  between 
wave  length  0.502  and  0.560  micron,  and  shall  show  a  maximum  value  of 
intensity  of  the  spectiiim  at  wave  length  0.55  micron.  The  above  values  are 
obtained  by  test  of  samples  at  the  nav}-^  yard,  New  York,  from  standards  made 
at  that  yard.  All  comparisons  and  verifications  of  these  values  and  testing  of 
samples  will  be  conducted  at  the  navy  yard,  New  York,  by  a  Government 
representative.  The  above  values  of  percentages  are  a  minimum  and  any 
increase  in  the  total  energy  below  wave  length  0.560  micron  wiU  be  considered 
satisfactory  and  advantageous. 

(6)   Color  ofjlame. 

The  color  of  flame  shall  show  general  characteristics  somewhat  similar  to 
that  of  the  an;,  except  that  the  maximum  point  of  intensity  shall  be  at  0.580 
micron,  and  the  per  cent  of  energy  in  the  flame  shall  not  show  more  than  10 


THE  SEARCHLIGHT. 


143 


per  cent  of  the  energy  of  the  total,  which  includes  the  crater,  flame,  and  carbon 
tips. 

(c)  Height  of  flame. 

The  height  of  this  flame  should  not  exceed  six  times  the  diameter  of  the 
positive  carbon. 

Samples. 

10.  Before  shipment  of  carbons  samples  must  be  submitted  for  test  to  the 
material  officer,  navy  yard.  New  York.  The  package  containing  these  samples 
shall  be  plamly  marked,  stating  the  size  of  carbons,  and  all  data  necessary  for 
identification.  Failure  of  the  samples  to  meet  any  of  the  above  requirements 
shall  be  deemed  sufiicient  cause  for  rejection  of  all  carbons  represented  by 
samples. 

Packing. 

11.  Carbons  shall  be  packed  for  shipment  in  tin  cans,  10  in  each  can, 
positives  and  negatives  separate.  They  will  be  so  -vvrapped  in  paraffined  paper 
or  other  waterproof  material  as  to  prevent  the  absorption  of  moisture  by  the 
carbons.  Cans  will  be  sealed  waterproof  and  in  such  a  manner  as  to  be  easily 
opened  and  resealed  at  will.  Each  can  will  be  plamly  and  completely  marked 
with  sufficient  data  to  facfiitate  the  identification  of.  the  contents. 

Specifications  for  60-inch  searchlight  carbons  are  not  given,  but  the 
above  specifications  in  general  apply  to  this  size  of  low-power  carbons.  The 
dimensions  of  60-inch  low-power  carbons  are  as  follows: 


Diameter. 

Length. 

Po'!itive 

Negative 

Inches. 
2 

IS 

Imlies. 
15 
12 

Navy  Department  Specifications. 

SEARCHLIGHT    CARBONS    FOR    USE    IN    THE    UNITED    STATES    NAVY. 

Janvary  8,  1918. 

General  specifications. 

1.  General  Specifications  for  Inspection  of  Material,  issued  by  the  Navy 
Department,  in  effect  at  date  of  opening  of  bids,  shall  form  part  of  these  speci- 
fications. 

General  description. 

2.  Carbons  shall  be  circular  in  cross  section,  uniform  in  diameter  for  the 
entire  length,  homogeneous  in  texture,  and  free  from  all  flaws,  cracks,  or 
impurities  which  may  cause  unsteady  burning.  The  carbons  covered  b}'  these 
specifications  are  of  two  classes,  known  as  the  3-to-2-ratio  and  the  1-to-l-ratio 
carbons.  These  terms  refer  to  the  rate  of  burning  of  positive  with  reference 
to  negative. 

Dimensions,  current,  and  arc  voltage. 

3.  The  tables  following  give  the  general  dimensions,  current,  and  arc  volt- 
age of  the  two  types  of  searchlight  carbons. 

C(U3S— IS 10 


144 


THE   SEAKCHUGHT. 
(a)  Dimension*  for  the  l-to-l-ralio  carbon*. 


PI'eof 
.teirch- 
Ught. 

Current 
amperes. 

Arc  volt- 
oge. 

Dimensions  in  millimeters. 

Positive 
diameter. 

Positive 
length. 

Neratlve 
diameter. 

Neeatlve 
length. 

Inclttt. 
9 
12 
18 
24 
30 
3« 

10 
20 
35 
50 
80 
120 

4ft-49 
48-51 
50-54 
£0-54 
5.5-59 
58-82 

13 
16 
16 
19 
25 
28.5 

105 
140 
ISO 
230 
2,'0 
2i0 

8 

9 

9 
10 
11.5 
13 

CO 
130 
ICO 
210 
230 
230 

(6)  Dimensions  for  the  3-to-S-ratio  carbons. 


Size  of 
search- 
light. 

Current 
amperes. 

Arc  volt- 
age. 

Dimensions  in  inches. 

Positive 
diameter. 

Positive      Negative      Neiative 
length.       diameter.       length. 

Incha. 

1^ 
18 
24 
30 
36 

10 
20 
35 
50 
SO 
110 

40-t5 
4(M5 
40-45 
43-48 
4.>-S0 
55-60 

1 

5 
6 

m 

12 
12 
12 

1                       7 

Negative  carbon. 

4.  (a)   For  1-to-l  ratio. 

The  negative  carbon  for  the  1-to-l-ratio  carbons  sliall  consist  of  a  cored 
carbon,  heavily  copper  coated  to  within  1\  inches  from  the  tip.  It  shall  be 
uniform  in  diameter  and  one  end  shall  be  tajiered  to  a  point  at  an  angle  of 
about  45  degrees.  The  <'arbon  shall  be  hard,  homogeneous  in  texture,  thor- 
oughly baked,  and  straight.  It  shall  be  free  from  any  imperfection  which  may 
cause  the  arc  to  hiss  or  flicker.  The  dimensions  for  carbons  for  various  sizes 
of  searchlights  can  be  found  in  table  forming  part  of  these  specifications. 

(b)   Ftw  3-to-2  ratio. 

The  negative  carbons  for  the  3-to-2-ratio  carbons  shall  consist  of  a  shell 
and  core,  the  shell  being  a  hard,  homogeneous  carbon  and  the  core  shall  be 
soft  carbon.  The  negatives  shall  be  copper  coated  to  within  1^  inches  of  end. 
The  dunensions  of  carbons  for  various  sizes  of  searchlights  can  be  found  under 
the  table  forming  part  of  these  si)ecifications. 

Positive  carbon. 

5.  The  positive  carbon  shall  consist  of  two  parts,  namely  the  shell  and 
the  core. 

(a)  Tie  shell.  * 

The  shell  shall  be  homogeneous  in  texture,  free  from  injurious  imper- 
fections, thoroughly  baked,  and  one  end  slightly  tapered,  with  a  crater  formed. 
The  composition  of  shell  must  be  such  that  combustion  shall  be  complete 
under  normal  conditions  of  operation. 

(b)  Tie  core. 

The  core  of  the  positive  carbon  shall  be  composed  of  a  hard,  white  flame, 
material,  of  uniform  circular  cross  section,  shall  run  evenly  in  the  center  of 
the  shell,  and  shall  be  so  fitted  in  the  shell  as  to  eliminate  any  spaces  between 


THE   SEARCHLIGHT. 


145 


it  and  the  shell  which  may  tend  to  cause  flickering  of  the  arc.  The  structure 
of  the  core  shall  be  such  that  it  shall  not  crumble  or  loosen  from  the  shell 
without  the  actual  breaking  of  the  shell  from  the  core.  The  dimensions  for 
various  sizes  of  searchlights  are  shown  under  table  forming  part  of  these 
specifications. 

Ratios  of  burning. 

6.  (a)  The  ratio  of  burning  of  the  carbons  known  as  the  1-to-l  ratio  shall 
be  approximately  1  part  by  length  of  positive  to  1  part  by  length  of  negative. 

(b)  The  ratio  burning  of  the  carbons  known  as  the  3-to-2  ratio  shall  be 
approximately  3  parts  by  length  of  positive  to  2  parts  by  lengths  of  negative. 

Performance  when  burning  under  normal  conditions. 

7.  The  carbons  when  burning  under  normal  operating  conditions  shall 
burn  with  a  minimum  of  flickering  or  sputtering  and  shall  not  crack  or  throw 
off  chips.  The  iiame  shall  not  be  excessive  and  the  composition  of  the  flaming 
material  shall  be  such  that  the  ash  deposit  wiU  not  impair  the  mechanical 
operation  of  the  lamp.  The  amount  of  soot  deposited  on  the  mirror  and  finders 
shall  not  be  great  enough  to  seriousl}'  impair  the  range  of  the  searchUght  during 
a  4-hour  period  of  continuous  operation. 

Minimum  candlepower. 

8.  The  foUowing  table  gives  values  of  the  candlepower  of  the  arc,  burning 
under  normal  conditions,  which  wiU  be  considered  a  minimum  acceptable  value 
at  maximum  point  of  distribution  curve  for  the  carbons  of  different  sizes  of 
searchhghts. 


Size  of 

sparch- 

3-to-2  ratio. 

1-to-l  ratio. 

ILSht. 

Candle- 

Candle- 

Ituhtt. 

power. 

power. 

9 

900 

1,500 

12 

2,200 

3,500 

18 

5,000 

7,500 

24 

9,000 

11,500 

30 

IS,  000 

20,000 

36 

25,000 

32,000 

General  characteristics  of  light  from  arc. 

9.  (a)   Color  of  crater  light  and  general  cJiaracteristics  of  beam. 

The  color  of  the  light  from  the  arc  when  operating  under  normal  condi- 
tions shall  appear  bluish  white  to  the  eye,  and  shall  show  color  characteristics 
and  distribution  of  intensity  identical  with  samples  previously  tested  at  the 
New  York  Navy  Yard,  records  of  which  can  be  had  by  apphcation  for  report 
No.  289  on  file  at  Navy  Department,  Bureau  of  Steam  Engineering,  Washing- 
ton, D.  C,  or  at  the  testing  laboratory,  machinery  division,  navy  yard,  New 
York. 

(6)  The  height  of  the  flame  above  the  positive  tips  shall  not  exceed  six 
times  the  positive-carbon  diameter. 

Samples. 

10.  Before  shipment  of  carbons  samples  must  be  submitted  for  test  to  the 
engineer  officer,  navy  yard,  New  York.    The  package  containing  these  samples 


146 


THE  SEARCHLIGHT. 


shall  be  plainly'  marked,  stating  the  size  of  carbons  and  all  data  necessary  for 
identification.  Failure  of  the  samples  to  meet  any  of  the  above  requirements 
shall  be  deemed  sufRcient  cause  for  rejection  of  all  carbons  represented  by 
samples. 

Packing. 

11.  Carbons  shall  be  packed  for  shipment  in  tin  cans,  20  in  each  can, 
positives  and  negatives  separate.  The}'  will  be  so  wTapped  in  parairined  paper 
or  other  waterproof  material  as  to  prevent  the  absorption  of  moisture  by  the 
carbons.  Cans  will  be  scaled  waterproof  and  in  such  a  manner  as  to  be  easily 
opened  and  resealed  at  will.  Each  can  will  l)e  plainly  and  complctel}'  marked 
with  sufficient  data  to  facilitate  the  identification  of  the  contents. 

SPECIFICATIONS   FOR   CARBONS   FOR    HIGH-INTENSITY   SEARCHLIGHTS. 

January  1,  1918. 

General. 

1 .  General  specifications  for  the  Inspection  of  Material  issued  by  the  Navy 
Department,  in  effect  at  the  date  of  opening  of  bids,  shall  form  a  part  of  these 
specifications. 

Description. 

2.  The  carbons  covered  by  these  specifications  shall  be  classed  under  two 
headings,  one  for  the  carbons  for  the  two  tj'pcs  of  lamps  manufactured  by 
General  Electric  Co.,  and  one  for  the  type  manufactured  by  the  Sperry  G3'roscope 
Co.  The  general  characteristics  of  the  carbons  are  identical,  the  positive  to 
consist  of  a  hard  plain  carbon  sheel,  uncoatcd,  with  a  core  of  flaming  material, 
and  the  negative  to  consist  of  a  hard  cai'bon  shell  and  soft  neutral  carbon  core. 

Dimensions. 

3.  The  dimensions  of  the  positive  and  negative  carbons  for  each  type  of 
lamp  as  noted  above  shall  conform  to  the  following  tables: 

(a)  General  Electrk  Co.  {Beck)  alcohol  and  air-cooled  lamps. 


Size  of 
search- 
light. 

Positive. 

Nceativo. 

l-iianieter 

of  shell 

(outside). 

Length. 

Pia  meter 

ol  shell 

(out.'-idc). 

Length. 

Inches. 
36 
30 
24 

IS 

Ivch. 
0.630 
.53.1 
.433 

Inches. 
44 
36 
IR 

Ircfi. 
0  «3 
.413 
.433 

Inches. 
13} 
12 

7 

(6)  Sperry  Gyroscope  Co.  lamps. 


Pi-e  ct 
search- 
light. 

Positive. 

Negati  e. 

Diameter 

ol  «hell 

(outside). 

Length. 

Diameter 

ofshrll 

(outside.). 

Length. 

Inches. 
36 
30 
24 
18 

Inch. 
0  630 

Inches. 
36 

Inch. 
0  4.^3 

Inches. 
12 

.433 

io 

.«3 

' 

THE   SEARCHLIGHT. 
(c)  Limits  of  allowance  for  positive  and  negative  diameter. 


147 


size  nf 
.searchlight. 

Positive  diameter. 

Negative 

diameter. 

Negati\  e 

coppered. 

Minimum. 

Maximum. 

Minimum. 

Maximum. 

Minimum, 

Maximum. 

Inches. 
36 
30 
24 

Inches. 

0  620 

.527 

.425 

Inches. 

0.r.40 

.547 

.433 

Inches. 

0  423 

.42i 

.423 

Inches. 

0.443 

.443 

.443 

Inches. 
0.428 

Inches. 
0  453 

.42S 

.453 

{d)  Core  diameters. 

Tlie  diameter  of  the  negative  core  shall  be  approximately  0.05  inch  and 
the  diameter  of  the  positive  core  shall  be  in  all  cases  one-half  the  outside 
diameter  of  the  positive  shell. 

The  positive  carbon. 

4.  (a)  SleU. 

The  positive  carbon  shell  for  both  tj'pes  of  lamps  shall  be  identical  and 
shall  consist  of  a  hard,  homogeneous  shell  of  neutral  carbon,  fine  in  texture, 
free  from  any  flaws,  cracks,  holes,  or  irregularities  in  roundness,  to  be  sufliciently , 
straight  over  its  enthe  length  to  pass  through  a  tube  12  inches  long,  and  having 
an  internal  diameter  of  0.031  inch  greater  than  the  maximum  allowed  diameter 
of  the  positive  shell.  The  rise  from  a  plane  surface  at  its  highest  point  shall 
not  exceed  0.25  inch.  The  shell  shall  be  circular  in  cross  section,  uniform  in 
thickness  for  its  entire  length,  and  the  core  centrally  located.  One  end  shall 
be  chamfered  3^  inch  deep. 

The  positive  core. 

(6)  The  core  shall  consist  of  a  hard  flaming  material  and  shall  run  central 
in  the  shell  for  its  entire  length.  It  shall  be  of  uniform  diameter,  homogeneous 
in  texture,  and  shall  contain  no  air  holes  or  spaces,  cracks  or  injurious  flaws, 
and  shall  be  so  applied  within  the  shell  as  to  be  secure  and  hard  enough  to  with- 
stand all  shocks  to  which  the  caibon  may  be  normally  subjected,  without 
crumbling  or  disintegrating. 

The  negative  carbon. 

5.  The  negative  carbons  to  be  of  two  types  described  and  specified  as 
follows : 

(a)   For  General  Electric  Co.'s  (BecJc)  alcolol  and  air  cooled  lamps. 

The  negative  carbon  shall  consist  of  a  hard,  homogeneous  shell  of  neutral 
carbon,  uncoated,  free  from  flaws,  cracks,  or  other  injurious  defects,  sufficiently 
straight  so  that  when  laid  on  a  plane  surface  with  one  end  held  do\^^l  the  other 
end  will  not  rise  more  than  0.08  inch  from  the  plane  surface.  Both  ends  of 
the  carbon  shall  be  beveled  about  70  degrees.  This  carbon  shall  be  cored  for 
the  entire  length  with  neutral  material,  applied  in  such  a  way  as  will  prevent 
crumbling  or  detachmg  from  shell. 

(6)   For  Sperry  Gyroscope  Co.'s  lavips. 

The  negative  carbon  shall  consist  of  a  hard,  homogeneous  shell,  or  neutral 
carbon,  free  from  flaws,  cracks,  or  other  injurious  defects,  sufficientlj-  straight 
so  that  when  laid  on  a  plane  surface  with  one  end  held  down  the  other  end 
will  not  rise  more  than  0.08  inch  from  the  plane  surface.     One  end  of  the  car- 


148 


THE   SEABCHUGHT. 


bon  shall  be  beveled  about  70  degrees.  The  carbon  shall  be  cored  for  the 
entire  length  with  neutral  material  applied  in  such  a  way  as  will  prevent 
crumbling  or  detaching  from  the  shell.  Tlic  carbon  shall  be  copper  coated  to 
within  H  inches  from  the  tapered  end  with  a  heavy  copper  plate,  uniform  in 
thickness,  smooth  of  surface,  and  of  such  thickness  as  to  show  an  ohmic  resist- 
ance of  0.0003  to  0.000.')  ohm  per  inch  of  length  of  the  finished  carbon. 

Performance  when  burning. 

G.  Tlie  carbuns,  when  ))urning  under  noniiiil  conditions,  shall  maintain  a 
dcej),  well-formed  crater.  The  arc  formctl  on  these  carbons  under  normal 
conditions  shall  be  steady  and  shall  not  emit  any  excessive  amount  of  soot  or 
other  substance  which  will  seriously  impair  the  reflective  qualities  of  the 
miiTor  or  the  transmission  qualities  of  the  front  door  strips  during  a  period 
of  eight  hours'  continuous  operation  with  the  ventilation  of  drum  normal. 
AMieu  l)urniiig  under  normal  conditions  the  carbons  shall  burn  with  very 
little  asli  anil  shall  not  throw  olT  chips.  The  candlepower  of  the  arc  for  the 
normal  sjiecified  operatuig  cunent  for  the  two  types  of  arcs  shall  show  a 
minimum  value  of  crater  light  and  a  minimum  horizontal  intensity  at  the 
maximum  point  of  the  distribution  curve,  conforming  to  the  following  table: 

.VLC0H0L-C00LEi>  LA.\I1'S. 


Size  or 
searcblight. 

Operating 
cnrront. 

.r^riii^'Si-"' 

Ma'-imiim 
Ilamf  and 

tip  in- 
tenMtv. 

at  30'. 

Inehrt. 

315 

30 

ISO 
120 

100,000            70,000 
70  000       

.30,000 

1 

AIR-COOLED  LAMPS. 


Size  of 
searchlight. 

Operating 
current. 

Vinimum 
total  hori- 
zontal can- 
dlepower 
8120°. 

Minimum 
crater 

inteiL^itv 
at  30=.' 

Maximum 
flame  and 
tip  in- 
tensity 
ai  20'. 

Inehet. 

30 
24 

150 
115 
75 

100,000 
70,000 
45,000 

50,000             50,000 

27,000    1         IR.OOO 

Life  per  trim. 

7.  The  life  per  trim  of  a  single  pair  of  carbons  shall  be  in  accordance  with 
the  following  table.  After  the  prescribed  time  there  shall  be  sufficient  length 
of  both  positive  and  negative  so  that  stubs  still  are  in  electrical  contact  with 
conducting  fingers. 


3G-inch 
searchlight. 

30-lnch 
searchlight. 

24-inch 
searchlight. 

2}  hours. 

2i  hours. 

IJ  hours. 

General  characteristics  of  light  from  arc. 

8.  The  color  of  the  beam  from  a  standard  searchlight  workhig  under 
normal  conditions  shall  appear  bluish  white  to  the  eye  and  shall  show  color 


THE   SEARCHLIGHT.  149 

characteristics  and  distribution  of  intensity  identical  with  samples  previously 
tested  at  the  New  York  Navy  Yard,  records  of  which  can  be  had  by  application 
for  report  No.  289  on  file  at  the  Na\y  Department,  Bureau  of  Steam  Engineering, 
Washington,  D.  C. 

Samples. 

9.  Before  shipment,  samples  of  material  to  be  supplied  on  the  contract 
must  be  submitted  to  the  engineer  officer,  navy  yard.  New  York,  for  test. 
The  packages  containing  these  samples  shall  be  plainly  marked  with  all  data 
necessary  for  identification  of  contents. 

Packing. 

10.  Carbons  shall  be  packed  for  shipment  in  tin  cans,  25  pairs  per  can, 
and  the  can  sealed  waterproof  in  such  a  manner  that  it  can  be  opened  and 
resealed  easily.  Each  can  shall  be  plainly  labeled  with  all  data  necessary  for 
identification,  stating  whether  for  General  Electric  Co.'s  alcohol  and  air-cooled 
lamps  or  for  Sperry  Gyroscope  Co.'s  lamps. 

Note. — The  General  Electric  Co.,  24  inch,  high-power,  air-cooled  searchlights  will  use  car- 
bons as  follows: 

Positive,  24  inches  lon^, 

NeLrative.  8J  inches  long, 
instead  of  lengths  of  IG  inches  for  positive  and  7  inches  for  negative  carbons  as  given  in  speci- 
tlcations.     The  time  of  burning  per  trim  is  greatly  increased  by  using  the  longer  carbons. 


The  navy  yard,  New  York,  has  tested  all  types  of  carbons  u^ed  in  the 
United  States  Nav3%  determining,  bj"^  spectrophotometer  analysis  of  the 
beams,  the  intensity  of  each  beam  in  each  part  of  the  spectrum.  The  results 
are  shown  in  a  series  of  curves  which  follow  th?  report  of  the  test  given  below. 
These  curves  form  a  basis  on  which  are  founded  specifications  governing  light 
characteristics  of  carbons. 

TEST  Xo.  289. 

TEST   OF    HIGH-POWER    AXU    LOW-P()WEI£    SEAKCHLIGIIT    CARBONS    TO    DETERMINE 
SPECTRUM    CHARACTERISTICS    OF    ARC    AND    RESULTANT    BEAM. 

March  14.   1917. 

1.  Tests  have  been  conducted  by  this  division  on  all  types  of  searchlight 
carbons  in  use  in  the  Navy  to  determine  the  spectrum  characteristics  of  each 
ty])e,  and  also  the  effect  of  the  color  of  the  arc  on  the  visibility  of  the  beam, 
the  arc  being  protected  tlu-ough  a  Navy  standard  silver-backed  glass  parabohc 
mirror. 

2.  Method. 

All  data  taken  was  calculated  from  results  obtained  from  a  Hilger  spectro- 
photometer. 

Before  starting  to  obtain  any  data  on  the  arcs  it  was  found  necessary  to 
have  standards  of  a  known  emission  curve  with  ordinates  in  such  convenient 
units  that  a  direct  comparison  between  the  total  visible  intensity,  and  the 
intensity  at  each  wave  length  of  the  spectrum  could  be  easily  found. 


150 


THE   SEAIiCHLIGnT. 


3.  A  brief  description  of  the  spectrophotometer  Is  as  follows: 
The  apparatus  consists  of  a  base,  fitted  with  two  colimeters,  placed  at  90- 
dcgrec  an<;lcs,  and  at  the  apex  is  mounted  a  standard  Lummer  Brodhum  prism. 
Each  colimeter  Ls  fitted  with  a  graduated  slot  at  its  outer  end  for  var^-ing  the 
intensity  of  the  light  on  the  prisms,  and  also  for  proper  concentration  of  the 
light  on  the  prisms.  Tliorc  is  also  fitted  a  four-sided  prism  termed  a  constant- 
deviation  prism,  mounted  on  a  revolving  table,  which  is  controlled  by  means 
of  a  micrometer  screw,  calibrated  to  read  directly  in  micron-.  In  front  of  this 
prism  is  mounted  a  telescope,  through  which  the  spectrum  is  viewed.  This 
telescope  is  also  fitted  with  symmetrical  slit,  whicli  forms  the  second  slot  of  a 
nonchromatic  illuminator  for  use  when  comparing  single  colors  of  the  spectrum. 

When  used  as  a  spectropho- 
tometer, thcimage  seen  through 
the  telescope  is  identical  with 
that  seen  tlirough  the  eyepiece 
of  a  Lummer  Brodhum  sight 
box,  the  light  from  the  one 
colimeter  being  thrown  on  the 
outer  field  and  that  from  the 
other  being  throMn  on  the  in- 
ner field.  By  varying  the  in- 
tensity of  the  standard  lamp 
in  the  usual  way  of  moving 
same  along  the  j)hotometer 
bench  until  the  fields  match 
in  intensity,  the  actual  inten- 
sity of  the  unkno\\'n  light,  the 
intensity  of  the  standard  of 
course  being  kno^vn  for  this 
color,  can  be  calculated  directly 
for  the  law  of  squares.  The 
constant  deviation  prism,  when 
once  calibrated  and  thecc)hme- 
ter.s  properly  set,  automatically 
throws  the  same  color  on  both 
fields  of  the  Lummer  Brodhum 
prism,  so  that  the  comparison 
of  any  or  all  parts  of  the  complete  spectrum  can  be  ea'^ily  made  by  simi)ly  turn- 
ing the  calibrated  micrometer  screw  to  the  wave  length  desired  and  balancing 
the  standard  lamp  till  the  fields  are  of  the  same  intensity. 

4.  Great  difiiculty  was  experienced  in  getting  a  standard  calibrated  in 
convenient  units  for  practical  use  in  the  comparing  of  the  arcs,  so  after  many 
attempts  to  have  this  work  done  outside,  an  attempt  which  finally  proved 
successful  was  made  at  this  yard. 

5.  The  standard  used  in  all  curves  and  data  submitted  are  calibrated  so 
that  the  ordinates  read  directly  in  international  candlepower  and  the  abscissa 
in  microns.  The  candlepower  is  only  comparative,  no  compensation  being 
made  for  absorption  of  the  lenses,  prisms,  diffusing  screens,  etc.,  used  in  the 


^*i9f*^mry  Sfa^darJ 


6* 

H/L6£fr  5P£CT/fOPH0rOMCT£fl 
5PeCTRUM  COMPAR/SOMoflAMn 


Fio.  151. 


THE  SEARCHLIGHT.  151 

photometer,  but  as  all  data  was  taken  under  the  same  conditions,  the  values 
of  the  ordinates  are  all  in  the  same  ratio  to  the  absolute,  it  only  being  neces- 
sary to  multiply  by  the  absorption  factor  of  the  apparatus  to  obtain  absolute 
values  in  international  candlepower  for  each  wave  length.  However,  compara- 
tive values  are  considered  ample  for  the  results  required,  so  no  attempt  was 
made  to  correct  to  absolute  units. 

6.  In  order  to  calibrate  the  standard  lamp,  the  spectrophotometer  was 
removed  from  its  mount,  and  one  colimeter  and  the  Lummer-Brodhum  prism 
removed,  allowing  the  light  admitted  through  the  slit  in  the  one  colimeter  to 
pass  directly  into  the  constant-deviation  prism.  This  light  was  then  viewed 
through  the  telescope  and  the  nonchromatic  adjusting  slots  in  the  telescope 
calibrated  to  correspond  to  the  wave  length  drum  on  the  constant-deviation 
prism.  Comparatively  small  slots  were  used,  both  on  the  colimeter  and  the 
telescope.  This  arrangement  was  found  to  project  a  single  color,  controlled 
directly  by  the  constant-deviation  prism  adjusting  drum,  out  from  the  eye- 
piece of  the  telescope.  The  arrangement  of  the  spectrophotometer  was  then 
mounted  on  end  of  a  standard  photometer  bench,  the  slot  of  the  eyepiece  of 
the  telescope  being  located  directlj"  over  the  standard  setting  for  the  test  lamp. 

7.  A  Schmitt  and  Haensch  flicker  photometer  was  then  located  on  the 
bench  in  a  stationary  mounting,  with  its  liitchie  wedge  just  2  inches  distant 
from  the  telescope  eyepiece,  the  eyepiece  being  considered  tlie  source  of  light, 
and  no  account  being  taken  of  the  distance  from  this  e3'epiece  to  the  lamp 
through  the  photometer.  As  only  comparative  results  were  sought,  this 
arrangement  was  considered  satisfactory. 

8.  A  movable  carriage  was  then  arranged  on  the  photometer,  upon  which 
was  mounted  a  32-candlepower  horseshoe-filament  standard  carbon-filament 
lamp,  this  lamp  being  considered  as  the  standard  by  which  all  intensities  were 
to  be  compared. 

9.  This  gave  an  arrangement  whereby  there  was  a  light  representing  the 
32-candlepower  standard  lamp  on  one  side  of  the  Ritchie  wedge  of  the  flicker 
photometer,  which  was  not  selective  for  any  particular  color,  but  gave  the  full 
spectrum  of  the  lamp  and  could  be  used  as  32  international  candles  from  which 
all  intensities  could  be  figured,  and  a  small  beam  rectangular  in  shape  on  the 
other  side  of  the  wedge  which  represented  the  intensity  of  the  slot  in  the  tele- 
scope the  color  of  which,  and  consequently  the  wave  length,  was  controlled  by 
the  constant  deviation  prism. 

10.  It  was  found  that  the  flicker  photometer  furnished  an  ideal  instiument 
for  the  comparison  of  these  two  different-colored  lights,  from  wave  length  0.71 
micron  to  about  0.53  micron,  which  runs  from  the  red  through  the  yellow  and 
partly  into  the  green.  Below  0.53  micron  the  difference  in  intensity,  due  to  the 
fact  that  the  carbon  lamp  is  essentialh'  an  orange  light,  and  consecjuently  the 
intensity  in  the  green  and  blue  part  of  the  spectrum  being  low,  it  was  found 
necessary  to  interpose  a  blue  screen  between  the  standard  lamp  and  the  photo- 
meter. This  screen  was  calibrated  for  the  transmission  factor  of  the  entu'e 
spectrum  of  the  carbon  lamp  without  any  regard  to  coloration  and  the  factor 
was  foimd  to  be  about  0.1,  so  that  below  wave  length  0.53  micron  the  standard 
intensity  was  taken  as  32  X  0.1  =3.2  international  candlepower. 


152  THE   SEARCHLIGHT. 

11.  It  was  desired  to  use  as  standards,  250-watt  tungsten  lamp,  rating  at 
about  200  international  candles.  Owing  to  this  comparatively  low  intensity, 
and  the  color  cliaractoristics  of  the  tungsten  lamp,  which  is  decidedly  a  yellow 
light,  it  was  found  very  difficult  to  obtain  an}'  reliable  readings  below  wave 
length  0.56  micron.  In  order  to  overcome  this  difficulty,  a  65-volt,  600-watt, 
nitrngen-iill(>d  tniiasten  lamp,  with  a  highly  concentrated  filament  wa^  used  as  a 
primary  standard  and  was  calibrated  by  the  comparison  of  each  part  of  the 
spectrum  with  the  standard  carbon  lamp,  with  and  without  the  color  screen,  as 
required,  and  tl.e  curve  fif  this  lamp,  when  computed  and  drawn,  was  the  primary 
standard  by  wliich  the  secondary  working  standards  were  calilirated. 

12.  After  the  a])ove  procedure  had  been  tried  and  the  results  carefully 
checked,  tlie  spectropliotometer  was  remounted  in  its  permanent  sotting  and 
the  secondary  standanls  calibrated  direct  through  the  photometer,  using  diffus- 
ing blocks  before  each  colimeter,  with  the  primary  standard  at  one  slot  and  tlie 
secondary  standard  to  be  at  the  other  slut  with  all  prisms  in  place,  and  each 
wave  length  of  the  standard  nitrogen-filled  lamj)  compared  with  the  250-watt 
tungsten  lamp,  and  from  this  data  a  curve  was  computed  showing  the  value  in 
intematioiial  candlepower,  neglecting  all  absorption  corrections,  for  each  part 
of  the  spectrum  of  the  250-watt  Mazda  lamps.  The  250-watt  Mazda  lamjjs  are 
used  as  the  working  comparison  standards  for  all  data  represented  by  the 
curves. 

13.  Although  the  inclosed  curves  show  nothing  absolute  as  far  as  intensities 
or  energy  characteristics  go,  and  are  probably  inaccurate  and  useless  from  any 
research  standpoint,  due  to  the  necessarily  large  unknown  absorption  prop- 
erties of  the  different  materials  used  in  the  diffusing  blocks  and  prisms,  the 
curves  thus  obtained  give  a  vcrj'  good  base  for  comparative  data  on  all  spec- 
trums.  This  also  necessitates  the  taking  of  any  future  comparative  data 
which  the  bureau  maj'  desire  on  this  particular  photometer,  using  this  method 
and  the  standards  which  are  here,  or  are  made  in  this  yard.  However,  it  is 
considered  that  some  very  interesting  and  instructive  results  can  be  obtained 
in  this  way,  whereby  a  method  is  furnished  of  comparing  the  present  product 
of  the  manufacturers  of  carbons  for  high  and  low  power  searchlights  with  those 
carbons  which  may  be  furnished  in  the  future. 

14.  Havuig  had  the  two  250-watt  tungsten  standards  previously  cali- 
brated at  the  Bureau  of  Standards  for  total  international  candlepower  and 
total  watts,  it  was  found  by  comparing  the  areas  of  the  spectrum  curves  of 
these  two  standard  lamps  that  the  ratio  of  the  area  covered  by  the  two  curves 
when  compared  with  the  ratio  of  the  total  intensity  of  the  lamps  was  almost 
identical,  thus  giving  ground  for  stating  that  the  ar(>a  of  the  curve  of  a  lamp 
taken  by  this  method  is  du-ectly  propoitional  to  the  total  visible  intensity  of 
the  lamp  in  inteniational  candlepower.  Thus,  in  the  data  taken  for  the  arcs, 
a  direct  method  is  supplied  of  comparing  the  total  visible  intensities  of  the 
respective  arcs  when  burned  on  certain  carbon.  These  curves,  for  convenience, 
may  be  called  emission  curves  of  the  arcs  formed  on  the  different  types  of 
carbons. 

15.  This  outlines  the  method  of  calibrations  of  standards  from  which  all 
comparisons  are  taken,  and  which  gives  a  base  for  all  discussions  and  formed 


THE  SEARCHLIGHT.  153 

in  this  report.     The  setting  of  the  apparatus  for  caUbrations  of  standards  and 
comparison  of  arcs  are  showm. 

16.  After  a  satisfactory  working  standard  had  been  obtained,  the  next 
step  was  to  apply  the  comparison  of  each  separate  wave  length  of  light  from 
the  standard  with  that  of  the  arcs. 

17.  The  arcs  were  set  up  at  a  distance  of  10  feet  from  the  test  colimeter, 
with  a  slot  opening  of  0.004  inch  and  the  slot  at  the  standard  opening  set  at 
0.050,  giving  a  reduction  ratio  of  12.5  to  1.  This  ratio  of  reduction  was  found 
adequate  for  the  low-power  arc,  but  the  high-intensity  arcs  required  the  inter- 
position of  a  sectored  disk  with  a  4-to-l  ratio  in  the  path  between  the  arc  and 
the  coHmeter  in  order  that  a  balance  could  be  obtained  with  this  light  from  the 
standard. 

IS.  Readings  were  then  taken  for  the  intensity  of  each  0.005  wave  length 
starting  at  0.44  micron  and  reading  as  high  as  possible  in  the  visible  spectrum. 
No  successful  attempt  was  made  to  take  any  data  outside  the  visible  spectrum, 
as  the  only  part  to  which  interest  is  attached  is  the  useful  visible  spectrum. 
Data  was  taken  on  all  types  of  36-inch  carbons  at  present  in  the  service,  but 
no  data  was  taken  on  any  other  sizes  as  this  data  really  only  gives  a  comparison 
between  the  light  from  the  new  high-power  lamps  and  those  of  the  old  low- 
intensity  type,  and  as  there  are  no  lamps  at  present  developed  smaller  than 
36  inches  in  the  high-power  type  no  tune  was  spent  on  taking  the  data  on 
smaller  low-power  lamps,  although  all  this  will  be  accomplished  hi  the  future. 

19.  It  is  an  established  law  that  the  light  from  the  part  of  the  spectrum 
represented  by  wave  lengths  0.54  to  0.56  micron,  inclusive,  is  the  light  which 
the  retina  of  the  eye  is  most  sensitive  to,  therefore  the  arc  most  desirable  for 
long  ranges  is  that  arc  which  shows  the  greatest  intensity  in  this  part  of  the 
spectrum;  but  from  experiment  it  has  been  found  that  when  the  light  from 
the  arc  is  projected  by  means  of  a  reflector,  this  reflector  has  absorbing  qualities 
for  certain  coloi-s.  In  the  Na%'3'  standard  searclilights  a  glass  parabolic  mirror 
is  used.  This  mirror  is  backed  with  silver  and  the  combination  has  been  found 
to  have  selective  quaUties  for  the  light  of  wave  lengths  higher  than  0.57  micron 
and  the  greatest  efficiency  of  transmission  at  the  green  part  of  the  spectrum 
between  0.54  and  0.56  micron  wave  length.  This  fact  accoimts  for  the  high 
efficiency  of  transmission  of  the  visible  spectrum  by  the  silver  mirror,  and 
this  fact  also  brings  out  the  reason  why  the  gold-backed  mirror  is  so  inefficient 
when  used  with  the  electric  arc  as  the  light  source. 

20.  With  the  above  facts  established,  it  is  evident  that  the  aim  should  be 
to  adopt  the  color  of  the  arc  to  give  its  highest  intensity  at  a  wave  length  of 
about  0.55  micron,  this  being  about  the  center  of  the  green  spectrum. 

21.  The  material  used  in  the  mirrore  is  the  best  obtainable  at  the  present 
time  for  efficient  light  transmission  at  the  point  of  highest  visibility,  so  that  the 
miiTor  question  can  be  left  for  the  present  time  as  satisfactory. 

22.  Results  from  the  experiments  show  that  the  low-power  arc,  although 
showing  a  fairly  high  candiepower  on  the  photometer,  is  very  rich,  in  the  wave 
length  greater  than  0.57  micron,  which  represents  colors  ranging  from  the 
yellow  up  to  the  red  and  shows  a  minimum  of  Ught  in  the  visible  spectmm 
below  0.57  micron,  which  runs  from  the  yellow  through  the  violet. 

23.  This  arc,  which  in  itself  does  not  give  the  maximum  Ught  at  the 
most  efficient  point,  when  pi-ojected  thi-ough  the  mirror  which  is  selective 


154 


THE  SEARCHLIGHT. 


above  wave  length  0.56  micron,  will  naturally  be  very  inefficient  and  necessarily 
have  a  short  range,  due  to  the  comparatively  small  amount  of  light  emitted 
below  wave  length  0.50  micron. 

24.  On  the  other  hand,  with  the  high-power  searchlight  lamp,  the  arc 
shows  its  greatest  intensitj'  at  wave  length  0.55.  Tliis  seems  to  be  a  particu- 
larly well-(le-;igncd  s))cctrum  for  use  with  the  Navy  standard  min-on-,  as  the 
higho-^t  i)oint  of  light  transnii.-^sion  of  the  mirror  and  that  of  the  spectrum  of 
the  arc  practically  coincide,  thus  making  the  transmission  of  (he  light  of  the 
arc  by  the  mirror  in  the  most  efficient  possible  waj-,  in  addition  to  having  this 
light  tran.^mitted  at  the  point  of  ma.ximum  emis,-ion,  that  is,  the  gi-eatest  amount 
of  light  generated  by  the  arc,  and  that  transmitted  bj-  the  mirror  is  at  such  a 
color  as  to  give  a  beam  with  its  highest  intensit}-  at  the  color  to  which  the 
retina  of  the  eye  is  most  sensitive,  'lliis  fact  has  much  to  do  with  the  gi'eatly 
increased  range  of  the  high-power  light  over  the  old  t}^)e  of  low-power  arc. 

25.  The  values  given  in  the  following  table  are  computed  from  the  areas 
of  the  curA'es  of  emission  of  the  spectrums  of  the  different  t3-pes  of  arcs  and 
show  the  percentages  of  emission  and  different-colored  light  in  different  parts 
of  the  spectrum,  and  also  the  eliiciency  of  the  mirror  for  different  parts 
of  the  spectrum  and  for  the  total  beam.  In  order  to  compare  the  beam  spec- 
trum with  the  arc,  it  was  necessary  to  reduce  the  intensity  of  the  beam  spectrum 
to  a  scale  con-esponding  to  the  arc  s|:ectrum.  The  intensity  can  not  be  com- 
pared by  the  area  of  these  curves,  but  the  percentages  of  the  colors  transmitted 
can,  thus  giving  the  efficiency  of  transmission  of  color  by  the  mirror.  Tor  con- 
venience, a  point  was  chosen  in  the  spectrum,  which  showed  the  highest 
efliciency  of  transmission  by  the  mirror,  and  the  mirror  at  this  point  was 
considered  to  have  an  efliciency  of  100  per  cent.  This  accounts  for  the 
curve  of  the  beam  touching  at  one  jioint  on  the  curve  of  the  arc.  Tlien  con- 
sidering this  point  100  per  cent  efficient,  the  other  colors  at  various  wave  lengths 
are  compared,  the  efficiency  being  figured  from  the  ratio  of  the  ordinates  at  the 
various  wave  lengths.  Of  course  the  assumption  of  the  100  per  cent  trans- 
mission at  one  point  is  only  comparative,  because  the  efficiency  wUl  not  be 
near  as  good  as  this,  due  to  the  energy  and  light  ab.^orption  by  the  glass  and 
silver  and  also  the  front-door  lens,  but  the  results  give  a  very  good  comparison 
between  the  transmission  efficiencies  at  different  parts  of  the  spectrum  of  the 
beam,  when  using  the  low  and  high  power  arcs  as  a  source  of  light,  and  trans- 
mitting the  light  through  the  glass  mirror  and  front  door  of  a  Navy  standard 
searchlight.     The  same  miri'or  was  used  in  all  cases. 

26.  Upon  investigating  the  emission  cur^-es  for  (he  s])ectrum  oi  the  differ- 
ent type  of  arcs  and  their  resultant  beams,  the  following  values  representing 
the  percentage  of  the  total  fight  in  the  visible  spectrum  were  found: 


Color. 

Wave  length. 

Beck. 

Spcrry. 

Navy  standard, 
plain. 

Navy  standard, 
white  flame. 

Per  cent 
in  ate. 

Per  cent 
in  Ixsam. 

Per  cent 
in  arc. 

Per  cent 
in  beam. 

Per  cent    Per  cent 
in  arc.    { in  beam. 

Per  cent 
in  arc. 

Per  cent 
in  beam. 

Vi  lot  and  blue 

Green 

0.44-0.5')2 
.512-  .ofi 
.56-  .512 
.592-  .014 
.  Cl-t-  .  70 

5.5 
36.5 
26.9 
16.0 
15.1 

5.5 
42.6 
20.7 
12.8 
12.4 

6.0 
36.2 
27.4 
15.4 
14.4 

6.0 
40.0 
26.2 
15.5 
12.3 

l.S            3.3 
30.0           35.8 
30.0            28.9 
20.0             17.3 
18.5            14.7 

3.3 
33.3 
29.0 
17.5 
16.9 

4.25 
38.3 

Ydhw 

0ran'.;e 

Red.: 

27.8 
16.0 
13.05 

THE  SEARCHLIGHT. 


155 


27.  From  the  foregoing  table,  it  is  apparent  that  the  high-power  type  of 
lamp  and  the  white-flame  tj^pe  carbon  for  the  old-type  lamps  are  much  more 
efficient  than  the  old-type  carbon. 

28.  The  greatest  efficiency  is  obtained  in  the  transmission  of  the  light  from 
the  arc,  when  the  intensity  characteristics  of  the  beam  conform  to  those  of 
the  arc.  This  condition  is  reached  when  the  characteristics  of  the  muTor  for 
the  transmission  of  hght  at  different  wave  lengths  are  such  that  the  emission 
curve  of  the  beam  would  follow  the  curve  of  the  light  source.  In  order  to 
accomphsh  this,  the  curve  of  the  transmission  of  light  by  the  miiror  would 
have  to  be  a  straight  hne.  As  the  mirroi-s  are  selective  for  color,  the  greatest 
efficiency  is  obtained  by  having  the  light  from  the  arc  at  its  gi-eatest  intensities 
at  points  where  the  transmission  by  the  mirror  for  these  colors  is  gi-eatest. 
With  the  new  type  of  flame  carbons,  both  for  the  high  and  low  power  arcs, 
this  condition  is  very  closely  approached,  the  highest  intensity  points  of  the 
arc  spectrum  being  at  the  point  of  greatest  efficiency  of  the  miri'or,  whereas 
with  the  old  type  of  carbons,  the  gi-eatest  amoimt  on  intensity  and  emission  of 
light  is  on  the  points  of  diminishing  efficiency  of  the  miiTor  for  transmission. 
ITius  the  emission  curve  of  the  beam  from  the  new-tj-pe  carbons,  both  high 
and  low  power  conform  fairly  close  to  the  emission  curve  of  the  arc,  while  with 
the  low-power  arcs,  the  beam  is  considerably  distorted. 

29.  The  results  given  in  the  table  are  an  average  of  several  observations 
and  are  considered  fairly  representative  of  what  may  be  expected  from  future 
carbons  of  the  same  composition  and  characteristics.  The  results  in  the  blue 
and  violet  part  of  the  spectrum  vary  considerably,  and  this  is  due  probably  to 
unknown  absorptions  of  the  various  parts  of  the  apparatus.  The  intensity  of 
the  blue  part  of  the  spectrum  Ls  very  low  compared  with  that  of  the  rest  of  the 
spectrum  so  that  eiTore  may  also  be  introduced  due  to  the  difficulty  of  balanc- 
ing these  very  low  intensities. 

30.  The  intensity  distiibution  of  the  Beck  beam  is  not  quite  so  desirable 
as  the  Sperry  beam  for  the  highest  efficiency  of  transmission  by  the  mirror. 
The  intensity  distribution  of  the  Sperry  beam  coincides  very  closely  to  that 
of  the  arc  in  intensity  at  the  points  of  highest  visibihty,  while  the  Beck  beam 
shows  slight  distortion  at  the  gi-een  part  of  the  spectrum.  This  is  probably 
due  to  the  color  of  the  flame  of  the  Beck  lamp  which  is  decidedly  orange  in 
color,  and  this  intensity  is  taken  as  part  of  the  totals  of  the  foregoing  table. 
The  Sperry  flame  shows  a  color  nearly  approaching  the  arc  so  that  the  distor- 
tion in  the  Beck  beam  may  be  due  to  the  flame  and  cool  carbon  tops. 

31.  Regarding  the  percentage  of  total  intensity  emitted  by  the  crater  and 
the  carbons,  the  following  table  shows  these  values,  expressed  in  percentage 
of  total  emission: 


Searchlight  arc. 

Percentage 
flame. 

Percentage 
crater  light. 

Navy  standard,  plain 

Nav'v  standard,  white  Qame. 
Sperrv  (at  30°) 

2 

6 
49 
28.8 

98 
94 
.■il 
71.2 

Beck  (at  30°) 

32.  Although  the  Sperry  arc  shows  a  much  smaller  percentage  of  crater 
Ught  than  the  Beck  arc,  this  is  not  considered  a  disadvantage,  as  it  has  been 


156 


THE   SEAnCHLIGHT. 


found  by  actual  experiment  that  the  hot  carbon  tips  of  the  Sperry  arc  are  u?e- 
ful  and  enter  into  the  beam.  With  the  Beck  arc,  the  tips  are  fairh'  cool  and 
thuri  do  not  radiate  nmch  light.  A\Tien  the  Sperry  arc  is  measured  -svith  con- 
sideration for  the  hot  tips,  the  arc  s-hows  about  72  per  cent  useful  illumination. 
This  is  true  if  the  following  con>iderations  are  taken.  Consider  the  s)  here  of 
aberrations  from  which  useful  light  emanates  as  being  3^  inch  in  diameter. 
Then  all  light  falling  within  this  sphere  is  ui-eful.  Much  of  the  hght  from  the 
crater  and  carbon  tips  of  the  Sperry  arc  wUl  fall  within  a  sphere  of  this  ;  ize  so 
that  it  is  feasible  to  coa^ider  these  carbon  tips  as  a  useful  source  of  illumination. 
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MffiRORS  FOR  SEARCHLIGHTS. 


focue  ANO  OOORCI  Of  \-ic»MT 
Rao-I 
Rad-Z 


Fia.  152. 


SEARCHUGHT  AHRRORS. 

The  United  States  Navy  cmplo}-s  two  types  of  niirrore  for  use  in  search- 
lights, namely,  Mangin  minors  and  parabohc  mirrors.  The  former  are  used 
only  in  small  searclilights  of  9  and  12  inch  diameters.  Mangin  mirrors  are 
much  more  easily  manufactured  than  are  parabolic  mirrors,  and  hence  are 

cheaper.  For  small  search- 
lights they  are  excellent,  but 
in  large  sizes  they  are  not 
nearly  as  satisfactory. 

The  principle  of  the  Mangin 
mirror  is  as  follows:  the 
curvature  of  the  surfaces  are 
such  as  to  correct  for  refrac- 
tion, caused  by  the  glass,  of 
light  rays  emanating  from  the 
focal  point,  and  to  finally  effect 
the  approximate  paralleling 
of  all  light  striking  the  mirror  and  emanating  from  the  focus.  Figure  152 
shows  path  of  light  rays  with  such  a  reflector.  * 

Tlie  Mangin  mirror  gives  a  beam  of  small  spread  and  fairly  good  results  are 
obtained  from  this  type  of  mirror  even  with  a  comjmrativcly  large  light  source. 
The  parabolic  mirror  uses  the  principle  of  the  Jparabola.'^  Any  Inline  drawn 
from  the  focus  of  a  parabola  to  the  curve  makes  an  angle  with  the  normal  equal 
to  the  angle  made  by  the  nor- 
mal \vith  a  line  parallel  to  the 
axis  of  abscissiE. 

This  is  shown  in  the  dia- 
gram (fig.  153). 

In  small  sizes,  up  to  about 
7  inches,  the  parabolic  mirror 
is  not  as  satisfactory  as  the 
Mangin  mirror,  though  it  is 
lighter. 

In  grinding  glass  for  mir- 
rors it  is  of  importance  that 
glass  used  be  free  from  stria- 
tions  or  tear  drops,  as  these  seriously  affect  the  optical  properties  of  the 
mirror.  The  explanation  for  these  striations  seems  to  be  that  they  are 
caused  by  particles  of  the  crucible  in  which  the  glass  is  melted  dissolving  in 
the  molten  glass.  When  poured,  they  produce  the  striae,  and,  being  optically 
verj-  different  from  the  glass,  produce  absorption  and  refraction  of  hght  which 
impairs  the  efficiency  of  the  mirror  when  present  in  large  quantities.  More- 
168 


■' RSi.'iS-'-'*-' '.-  ''r-''hyf^-*^i'°^ff^ 


Or    Uk^mt 


Fio.  1S3. 


THE  SEABCHLIGHT. 


169 


over,  they  weaken  a  mirror  mechanically  because,  being  of  a  different  substance 
and  having  a  different  coefficient  of  expansion,  they  set  up  internal  stresses 
during  the  heating  or  cooliug  of  the  glass. 

Bubbles  in  the  mirrors  are  not  very  serious  as  they  have  little  effect  on 
either  the  mechanical  or  optical  properties  of  the  glass. 

The  most  desirable  glass  for  searchlights  is  one  which  would  have  the 
optical  properties  of  the  white  glass  now  used  and  the  mechanical  properties 
of  "Pyrex"  glass  so  much  used  for  cooking  utensils.  "Pyrex"  has  a  very 
low  coefficient  of  thermal  expansion,  so  low,  in  fact  that  it  may  be  heated 
quite  hot  and  plunged  into  cold  water  without  causing  it  to  shatter.  "Pyrex,'' 
however,  is  not  a  good  optical  glass. 

Work  is  being  done  to  produce  a  glass  equally  as  good  optically  as  any 
glass  used  at  present,  with  a  coefficient  of  expansion  approaching  that  of 
"Pyrex." 

Searchhght  mirrors  require  constant  care  to  keep  them  up  to  the  required 
point  of  efficiency.  They  should  be  wiped  and  dusted  frequently,  particularly 
where  particles  deposited  are  on  the  surface  of  the  glass  which,  if  allowed  to 
remain,  would  destroy  the  accuracy  of  the  surface. 

Following  are  specifications  for  Navy  searchlight  mirrors: 

17M7 


1918 


Navt  Department  SPEcmcATioNs. 


MANGIN   MIRRORS   FOR   SEARCHLIGHTS   IN  THE   UNITED   STATES   NAVT. 

General  specifications. 

1.  General  Specifications  for  Inspection  of  Material,  issued  by  the  Navy 
Department,  in  effect  at  the  date  of  opening  of  bid,  shall  form  a  part  of  these 
specifications. 

Description. 

2.  The  mirror  shall  consist  of  a  glass  plate,  the  respective  radius  of  the 
faces  of  which  shall  conform  to  Mangin's  determinations  of  same,  a  reflective 
backing,  and  a  protective  backing. 

Dimensions. 

3.  The  over-aU  dimensions,  thickness  of  glass  plate,  focal  length,  etc.,  of 
mirror  for  various  sized  searchlights  shall  conform  to  this  table  and  sketch, 
forming  a  part  of  these  specifications: 

[Ail  dimensions  in  inches.] 


SiMof 
minor. 

A. 

1 

B. 

c. 

D. 

E. 

F. 

9 

8^' 

m 

9 

lA 

H 

4.125 

12 

11^ 

12H 

12 

2H 

H 

6.10 

'              18 

I 

19A 

18 

% 

lA 

8.625 

Glass  plate. 

4.  The  glass  plate  shall  be  made  of  the  finest  grade  of  clear  glass  without 
perceptible  tint,  free  from  flaws,  bubbles,  and  other  defects,  and  shall  be  gromid 


170 


THE  SEABCHLIQHT. 


to  a  true  surface,  highly  polished,  front  and  back.     The  ratio  of  the  radii  of 
the  front  and  back  surfaces  shall  be  such  as  to  give  a  minimum  beam  dispersion. 

Reflective  backing. 

5.  The  reflective  backing  shall  consist  of  a  heavy  coat  of  metallic  silver. 
It  shall  be  homogeneous,  evenly  applied  to  the  surface  of  the  glass,  and  be  so 
fitted  as  to  form  an  air-tight  joint  between  it  and  the  glass.  The  backing  shall 
be  such  that  it  will  prevent  the  admission  of  air  or  any  foreign  substance 
between  it  and  the  glass  which  will  cause  oxidization  of  the  reflective  surface. 

Protective  backing. 

6.  Over  the  reflective  backing  shall  be  placed  a  protective  backing  con- 
sisting of  one  heavy  coat  of  metallic  copper,  and  over  this  copper  plate  a  coat- 
ing of  heavy  enamel  which  shall  so  seal  the  backing  as  to  render  it  absolutely 
waterproof  and  air-tight. 


Focoo 


Ra.d-1 


Rao-Z 


Fio.  154.— Dimension  diagram.    ifaii?ln  mirrors. 

Tests. 

7.  The  mirror  shall  be  required  to  meet  all  of  the  following  tests : 

(a)  BacHng. — The  backing  shall  not  be  afl"ectcd  by  either  sea  water, 
boiling  fresh  water,  or  a  dry  temperature  of  65°  C.  (150°  F.).  The  backing 
shall  be  subjected  to  each  of  these  consecutively  for  a  period  of  72  hours. 
The  enamel  paint  shall  be  of  such  material  as  not  to  be  readily  rubbed  off  at 
a  dry  temperature  of  65°  C,  or  when  moistened  with  sea  water. 

In  the  event  that  the  backing  proposed  has  not  previously  been  approved 
by  the  Bureau  of  Steam  Engineering,  the  contractor  will  be  required  to  submit, 
prior  to  delivery,  a  sample  mirror,  approximately  8  by  8  inches,  to  the  New 
York  Navy  Yard  for  test,  this  sample  to  be  backed  with  the  material  which  he 
proposes  to  furnish. 

(6)  Line  or  screen  test. — The  reflection  from  the  mirror  of  straight,  hori- 
zontal, and  vertical  intersecting  lines,  forming  1-inch  squares  on  a  screen,  shall 


THE  SKAECHUGHT. 


171 


be  photographed  and  this  photograph  shall  show  the  mirror  to  be  free  from 
any  irregularities  of  grinding  or  polishing. 

(c)  Sun  or  zone  test. — A  photograph  of  the  reflected  rays  of  the  sun,  when 
the  mirror  is  placed  at  right  angles  to  the  rays  of  the  sun,  shall  show  a  cone  of 
sharp  outline  and  weU-defined  apex.  The  diameter  of  the  sphere  of  aberra- 
tions shall  not  exceed  }4  inch. 

(d)  Beam.— -The  reflected  beam  from  the  mirror  when  a  concentrated 
filament  lamp  is  placed  at  its  focal  center  shall  be  round,  free  from  zones,  and 
the  quantity  of  useless  dispersed  rays  shall  be  negligible. 

(e)  NigJd  illuminating  tests. — The  tests  for  the  acceptance  of  the  mirror 
shall,  at  the  Government's  option,  include  a  night  illumination  test,  consisting 
of  placing  the  muTor  in  a  searchlight  and  using  the  searchlight  arc  lamp  for 
the  som-ce  of  light.  Tliis  test  shall  show  the  beam  to  be  of  a  uniform  intensity, 
decreasing  from  center  to  outer  edge  and  free  from  light  zones.  The  shape  of 
the  projected  beam  shall  be  a  true  circle  and  its  edges  clearly  defined. 

(/)  All  of  the  above  tests  shall  be  conducted  by  a  Government  representa- 
tive and  the  failure  of  the  mirror  to  meet  any  one  of  the  above  tests  or  require- 
ments shall  be  deemed  sufiicient  cause  for  its  rejection. 
Shipments. 

8.  Each  mirror  shaU  be  secm'ely  packed  in  a  separate  case  and  case  shall 
be  plainly  marked  with  all  data  necessary  to  give  complete  information  as  to 
its  contents. 

Specifications,  where  obtainable. 

Note. — Copies  of  the  above  specifications  may  be  obtained  upon  application  to  the 
Bureau  of  Supplies  and  Accounts,  Navy  Department,  Washington,  D.  C. 

Navy  Department  Specitications. 


PABABOLIO    SEAKCHLIGHT    MIRKOR3     FOB    USB    IN    THE    UNITED    STATES    NAVY. 

June  1, 1917. 

General  specifications. 

1.  General  Specifications  for  Inspection  of  Material,  issued  by  the  Navy 
Department,  in  effect  at  date  of  openmg  of  bids,  shall  form  part  of  these  speci- 
fications. 

Description. 

2.  The  mirror  shall  consist  of  a  glass  parabolic  plate,  a  reflective  backing, 
and  a  protective  backing. 

Dimensions. 

3.  The  over-all  dimensions,  thickness  of  plate,  focal  length,  etc.,  of  mirrors 
for  various  sizes  of  searchlights,  shall  conform  to  this  table  and  sketch,  forming 
a  part  of  these  specifications: 


Size  of  search- 
light (Inches). 


11>. 

18... 
24.. 
30... 
36... 


Uirror  dimensions  In  Inches. 

F 

Q 

H 

I 

J 

WH 

11 

H 

2H 

4 

19A 

19A 

^ 

■■w. 

m 

25!^ 

25ii 

Vf 

4A 

10 

31A 

31H 

rt 

6H 

ua 

37 

* 

BM 

UH 

>  The  11-inch  mirror  is  for  installation  in  incandescent  lamp  searchlight.    This  mirror  shall  be  of  best  commercial  type. 
Slight  Taraltions  from  the  dimensions  specified  will  be  permitted. 


172 


THE  SEABCHLIGHT. 


Parabolic  plate. 

4.  The  parabolic  plate  shall  bo  niado  of  the  finest  grade  of  clear  plate 
glass,  without  perceptible  tint,  free  from  all  flaws,  bubbles,  striae,  and  other 
defects.  It  shall  be  ground  to  a  true  parabolic  surface  on  both  front  and  back, 
the  focal  center  specified  being  made  the  focus  of  the  convex  surface  and  the 
concave  surface  being  ground  parallel  to  the  convex  surface.  The  thickness 
of  glass  shall  be  uniform  over  the  entire  surface,  and  all  dimensions  shall  con- 
form to  those  set  forth  in  table  forming  part  of  these  specifications. 
Reflective  backing. 

5.  The  reflective  backing  shall  consist  of  a  heavy  coat  of  metaUic  silver. 
It  shall  be  homogeneous  and  evenly  applied.  The  backing  shall  be  such 
that  it  will  prevent  the  admission  of  any  foreign  substance  between  it  and  the 
glass  which  will  cause  oxidization  of  the  reflecting  surface. 


FiQ.  155.— Dimension  diagram,    parabolic  mirrors. 

Protective  backing. 

6.  (a)  Over  the  reflective  backing  shall  be  placed,  electrolytically,  a 
heavy  coat  of  motaUic  copper  of  such  a  thickness  as  to  reinforce  the  reflective 
backing  and  protect  same  from  mechanical  injury. 

(6)  Over  this  copper  backing  shall  be  placed  one  or  more  coats  of  a  paint 
or  enamel  of  such  quaUty  as  to  render  the  greatest  resistance  possible  to  the 
admission  of  any  moisture  or  gases  which  may  injure  either  the  copper  or 
silver  backing.  The  gases  encountered  wUl  be  the  usual  flue  gases  given  off 
from  soft  coal  and  fuel  oil  purchased  under  naval  specifications  for  use  aboard 
ships  of  the  Navy. 
Tests. 

7.  (a)  Before  acceptance,  and  at  the  discretion  of  the  Bureau  of  Steam 
Engineering,  the  mirror  will  be  submitted  to  the  following  tests : 

(6)  Backing. — The  backing  shall  not  be  affected  by  either  sea  water, 
boiUng  fresh  water,  or  a  dry  heat  of  90°  C.  The  backing  shall  be  subjected 
to  each  of  these  consecutively  for  a  period  of  72  hours.     In  addition  to  this, 


THE  SEAECHUGHT.  173 

the  protective  backing  will  be  subjected  to  the  appUcation  of  hydrogen  sulphide 
gas,  washed  and  dried,  appUed  over  the  entire  surface  of  the  mirror  for  a  period 
of  6  hours.  At  the  end  of  this  period  the  reflective  backing  must  not  show 
the  least  signs  of  sulphiding,  the  copper  must  not  show  any  signs  of  discolora- 
tion, or  the  paint  must  not  be  affected  beyond  the  surface. 

(c)  In  the  event  that  the  backing  has  not  been  previously  approved  by 
the  Bureau  of  Steam  Engineering,  the  contractor  will  be  required  to  submit 
to  the  New  York  Navy  Yard  for  test  and  approval,  prior  to  opening  of  bids, 
a  sample  parabolic  mirror,  12  inches  or  more  in  diameter,  backed  with  the 
material  which  he  proposes  to  furnish. 

(d)  Line  test. — The  reflection  from  the  mirror  of  straight  horizontal  and 
vertical  intersecting  hnes  forming  1  inch  square  on  a  screen  shall  be  photo- 
graphed and  this  photograph  shall  show  the  mirror  to  be  of  uniform  thickness 
of  glass,  free  from  aU  irregularities  in  grinding,  striaj,  and  bubbles. 

(e)  Focal  center. — The  reflection  of  a  beam  of  Ught  1  inch  in  diameter, 
projected  perpendicular  to  the  directrix  of  the  parabola  and  reflected  through 
center  of  the  mirror  when  moved  across  the  mirror  of  any  diameter,  shall 
indicate  a  spherical  aberration  of  not  greater  than  ^  inch.  This  shall  be 
determined  photographically,  and  shall  be  taken  on  each  mirror.  Tests  will 
be  made  on  not  less  than  two  diameters,  90°  apart. 

(/)  Efficiency. — The  efficiency  of  transmission  of  the  Ught  from  a  250- 
watt  concentrated  filament  incandescent  lamp,  with  filament  on  focal  center 
of  mirror,  shall  show  not  less  than  70  per  cent  of  the  entire  energy  of  the  fight 
of  the  lamp  falling  on  the  mirror,  and  shall  show  a  transmission  of  not  less  than 
70  per  cent  for  fight  at  a  wave-length  of  0.510  micron  (green  fight)  and  an 
efliciency  of  not  less  than  76  per  cent  for  Ught  on  wave-length  0.540  micron 
(green  fight). 

(g)  Night  illumination. — The  tests  for  the  acceptance  of  the  mirrors 
shall,  at  the  Government's  option,  include  a  night  Ulumination  test,  consisting 
of  placing  the  mirror  in  a  searchfight  and  using  the  searchlight  arc  lamp  for 
the  source  of  fight.  This  test  shall  show  the  beam  to  be  of  a  uniform  intensity 
decreasing  from  center  to  outer  edge  and  free  from  fight  zones.  The  shape  of 
the  projected  beam  shaU  be  a  true  circle  and  its  edges  clearly  defined. 
Eejection. 

8.  All  of  the  above  tests  shaU  be  conducted  by  a  Government  repre- 
sentative, and  the  failure  of  the  mirror  to  meet  any  one  of  the  above  tests  or 
requirements  shaU  be  deemed  sufficient  cause  for  its  rejection. 
Shipment. 

9.  Each  mirror  shall  be  securely  packed  in  a  separate  case  and  case  shall 
be  plainly  marked  with  all  data  necessary  to  give  complete  information  as  to 
its  contents. 

Mirrors  whose  backing  is  damaged,  but  whose  sTirfaces  and  cm-ves  are  not 
impaired,  may  be  resdvered  and  made  equal  to  new  mirrors  by  the  process 
given  below. 

EESILVERING   PARABOLIC    SEARCHLIGHT   MIRRORS. 

1.  The  backing  paint  is  first  removed  by  immersing  the  back  of  mirror  in 
solution  of  potash  and  water.  (Three  pounds  of  potash  to  8  gaUons  of  water, 
approximately;  time,  3  hours;  is  usuaUy  found  to  be  sufficient.) 


174  THE  SEABCUUQHT. 

2.  Rinse  with  water. 

3.  Place  mirror  in  trough  for  cleansing  and  silvering. 

4.  Remove  old  silver  with  nitric  acid,  use  absorbent  cotton  on  wood 
Btick,  rubbing  carefully  over  surface. 

5.  Cleanse  thoroughly  with  water. 

6.  Wash  the  surface  with  ammonia  and  water  mixed,  to  remove  grease 
from  surface  to  be  silvered.     Use  absorbent  cotton. 

7.  iVgain  cleanse  thoroughly  with  distilled  water. 

8.  Cleanse  surface  with  absorbent  cotton  dipped  in  nitric  acid;  rinse  with 
distilled  water. 

9.  Apply  sUver  and  reducing  solutions.  Special  fixtures  are  fitted  to 
place  bottles  of  silver  and  reducing  solution  above  mirror  to  be  silvered. 
These  bottles  are  furnished  with  stop  cocks  to  regulate  flow  through  glass 
fumiel.  Distilled  water  is  run  through  rubber  tube  into  funnel  to  mix  with 
silver  solution  in  order  to  give  better  How  over  parabohc  surface. 

10.  Should  brownish  streaks  appear,  stop  flow  of  silver  and  reducing 
solutions.  ^Vllow  water  to  run,  rub  surfaces  carefully  with  absorbent  cotton. 
Start  silver  solution  again,  as  soon  as  the  dirt  has  been  removed. 

Note. — Care  must  be  takeu  that  the  cotton  used  is  perfectly  clean. 

11.  As  soon  as  the  silver  solution  is  appUed,  the  mirror  should  be  placed 
in  copper  bath  to  receive  the  necessary  coating  of  copper. 

Note. — Surface  to  be  silvered  should  be  kept  wet  constantly,  until  silvering  and  copper 
plating  is  completed. 

12.  For  30  and  36  inch  mirrors  about  30  minutes  is  usually  the  time  given 
for  copper  plating  the  silvered  surface. 

13.  Mirror  removed  from  plating  bath  should  be  washed  thoroughly  with 
clean  water. 

14.  Use  filter  paper  to  dry  mirror  surface  as  soon  as  removed  from  water 
bath.  The  paper  must  be  used  as  a  blotter,  and  is  not  to  be  rubbed  over 
the  surface. 

15.  The  first  coat  of  backing  paint  is  sprayed  on  and  baked  in  a  tem- 
perature of  about  250°  F.  for  about  three  hours.  For  the  first  coating,  red 
mirror  hack  paste  is  used  with  good  result,  followed  with  three  coats  of  Valspar 
varnish,  each  coat  baked  on  as  given  above. 

16.  Any  paint  spots  on  concave  side  can  be  removed  with  xylol  or  ben- 
zine. Use  absorbent  cotton  and  clean  linen  cloth  to  dry.  Rub  surface  with 
absorbent  cotton  and  nitric  acid.  Wash  with  soapy  water.  Dry  thoroughly 
with  clean  linen  cloth. 

Note. — It  is  important  that  no  other  than  distilled  water  is  used  at  any  time  during 
entire  process. 

TBAY   METHOD   FOE   SILVEEING   jnEBOBS. 

1.  Dissolve  4  ounces  silver  nitrate  crystals  in  150  cubic  centimeters  of 
distilled  water. 

2.  Take  4  gallons  of  distilled  water,  add  125  cubic  centimeters  silver 
nitrate  solution  given  in  paragraph  1.  This  solution  will  turn  muddy  in  color. 
Remaining  portion  of  silver  nitrate  is  kept  in  reserve. 


THE   SEABCHLIGHT. 


175 


3.  To  the  above  solution  add  C.  P.  ammonia  until  precipitate  which  first 
forms  redissolves.  Stir  well  with  glass  rod.  Stop  adding  ammonia  as  soon 
as  solution  begins  to  turn  clear. 

4.  Add  a  solution  of  2  ounces  (dissolved  in  water)  of  potassium  hydroxide 
C.  P.  alcohol  sticks.     The  solution  will  again  turn  muddy  in  color. 

5.  Again  add  C.  P.  ammonia  to  redissolve  the  precipitate.  As  soon  as 
solution  begins  to  turn  clear  stop  adding  ammonia.     Stir  weU  with  glass  rod. 

6 .  A  silver  kept  in  reserve  until  solution  turns  straw  color.  Stu-  well 
while  mbdng.  Add  distilled  water  to  this  reserve  solution  before  pouring  into 
solution  in  paragraph  5. 

7.  The  above  quantity  of  solution  wiE  silver  sui'face  of  approximately 
6,270  square  cubic  meters. 

8.  The  silver  crystals  and  potassium  hydroxide  must  be  dissolved  in  water 
in  separate  vessels. 


<=l-/\€>6   Stop    Cocks 


30TTUE.     doNTAlMlKIO. 


—  BciTTUe  <COMTAlM\NC» 


-* CSUASS  KuK/NE.>- 


Dl  £>T>V,V.E.O  WATER  - 


Mirror 


—  Rvj&BER  Tube. 


— Wood  TroooW 


DrfxikI 


FiQ.  155.— Arrangomeat  of  apparatus  for  resUvering  mirrors. 
REDUCING    SOLUTION    FOR   SILVERING   MIRRORS. 

1.  Mix  4^  pounds  of  granulated  sugar.  Eight  gallons  hot  distilled  water, 
110°  to  130°  F.  80  cubic  centimeters  C.  P.  nitric  acid.  Stu*  well  while  mixing. 
This  solution  must  be  kept  in  weH-corked  bottles. 

2.  If  this  solution  is  made  up  with  cold  instead  of  hot  water  it  must  stand 
10  days  before  using. 

3.  The  solution  made  up  as  in  paragraph  1  can  be  used  immediately. 

TO   CLEAN    SURFACES   OF    SEARCHLIGHT   MIRRORS. 

1.  To  prevent  scratching  use  absorbent  cotton  saturated  with  wood 
alcohol;  dry  with  clean  hnen  cloth. 

2.  At  the  factory  ammonia  is  used  a  great  deal,  although  wood  alcohol 
will  do  as  well. 

66438—18 12 


CHAPTER  14. 
CARE  OF  MODERN  HIGH-POWER  SEARCHLIGHTS  AND  CONTROL  GEAR. 


CARE  OF  MODERN  fflGH-POWER  SEARCHUGHTS. 

Tlie  advent  of  the  high-power  searchlight  has  materially  increased  the 
importance  of  the  application  of  searchlights  to  naval  work.  The  low-power 
scarchliglit,  while  excellent  for  navigational  purposes,  was  of  comparatively 
little  use  as  an  aid  to  gunnery  except  at  very  short  ranges.  It  is  hclievcd, 
however,  that  high-power  searchlights,  when  properly  used  in  connection  with 
broadside  guns,  will  materially  increase  the  efTcctivcness  of  these  guns,  and  it 
is  quite  possible  that  they  will  be  called  upon  for  use  during  the  firing  of  main- 
battery  guns. 

Low-power  searchlights  did  not  require  nor  receive  very  carefid  use  or 
attention.  High-power  scarchliglits,  with  their  many  comparatively  delicate 
parts  and  additional  refinements,  when  instaUcd  on  naval  vessels  received 
no  more  care  than  the  old  low-power  lights.  Conse(|Ucntly  gears  became 
damaged  and  stuck  with  paint,  pins  holding  gears  to  shafts  have  frequently 
been  sheared  off,  and  the  broken  pins  replaced  by  nails.  These  pins  were 
sheared  off  by  operators  attempting  to  forcibly  turn  the  searchlight  when  the 
control  shafts  were  locked  in  position.  An  operator  trying  to  turn  a  search- 
light and  finding  he  can  not  do  it  all  too  often  docs  not  look  for  the  reason,  but 
gets  some  one  else  to  help  him  turn  it.  Together  they  turn  the  light,  but  it 
turns  only  at  the  expense  of  pins,  gears,  shafts,  and  bearings.  Something  had 
to  break  before  the  searchlight  would  turn. 

Carelessness  in  details,  such  as  cleaning,  painting,  oiling,  and  operation, 
has  resulted  in  the  dcvelopnjent  of  much  backlash  and  lost  motion  in  con- 
trol of  mechanism,  grounds  and  short  circuits  became  frequent  occurrences, 
and  lights  did  not  operate  satisfactorily  and  deteriorated  rapidly. 

Present  high-power  searchlights  are  entirel)'  diflcrent  from  the  old  search- 
lights, which,  by  comparison,  are  Icnown  as  "low-power  searchlights."  Their 
mechanisms  are  more  complicated  and  their  construction  and  design  carried 
out  vnth  much  greater  accuracy  throughout.  So,  too,  are  the  newer  types  of 
control  gears,  designed  especially  to  ojjerate  with  the  greatest  smoothness  and 
accuracy.  They  are  made  with  a  care  commensurate  with  the  refinements  of 
the  machines  to  which  they  are  to  be  applied.  There  is  now  being  developed 
in  this  country  for  the  Navy  a  system  of  control  of  searchlights  on  battleships 
and  destroyers  similar  to  the  foUow-the-pointer  sj-stem  of  control  of  guns. 
Other  s}-stems  of  follow-the  pointer  control  of  searchlights  are  in  use  in  the 
navies  of  foreign  countries  and  are  developed  to  a  high  point  of  efficiency. 
Experience  has  shown  that  the  belligerent  nations  on  both  sides  have  for  some- 
time controlled  their  searchhghts  with  great  accuracy  by  some  S3stem  of  this 
kind.  Particular  care  is  therefore  necessan,-  to  keep  searclilights  and  their 
control  sj'stems  at  the  highest  obtainable  point  of  efficiency. 
176 


THE  SEAKCHLIGHT.  177 

Following  are  a  number  of  items  which,  if  observed,  will  aid  greatly  in 
obtaining  efficient  cooperation  between  guns  and  searchlights  at  night  and  the 
maximum  efficiency  of  the  searchlights  at  all  times: 

1.  Trained  men. 

Men  shoidd  be  trained  thoroughly  in  the  care  and  operation  of  searchlights. 

2.  Frequent  drills. 

Use  of  searchlights  in  connection  with  the  follow-the-pointer  system, 
opening  shutters  only  after  searchlights  are  trained  on  target. 

3.  Study. 

The  men  in  charge  should  thoroughly  know  their  equipment.  If  the}^  do, 
they  win  appreciate  its  refinements  and  the  necessary  care  in  operation  will  be 
easy  to  obtain.  The  instruction  booklets  furnished  with  searchlights  should 
be  carefidly  studied  by  men  charged  with  the  care  of  searchlights. 

4.  Backlash  and  lost  motion. 

When  these  develop  it  is  important  that  immediate  steps  be  taken  to 
carefully  align  and  adjust  gearing  to  remove  them. 

5.  Paint. 

A  frequent  cause  of  lost  motion  when  applied  to  wearing  surfaces,  particu- 
larly to  the  teeth  of  gears.  Occasionally  oil  holes  have  been  painted  over, 
paint  even  being  put  into  the  holes. 

6.  Lubrication. 

Some  gear  boxes  and  searchlight  bases  are  packed  in  grease.  These  should 
occasionally  be  examined  and  repacked  where  necessary.  Where  oil  is  used  it 
should  be  used  liberally  and  frequently.  Graphite  should  be  used  frequently 
on  exposed  gears. 

7.  Grit,  sand,  dirt,  etc. 

In  oil  or  gi'case  these  quickly  destroy  accuracy  of  gears,  bearings,  and 
wearmg  surfaces.  Great  care  should  be  taken  to  keep  searchlight  gears  and 
electric  apparatus  free  of  abrasives. 

8.  Dampness. 

Electric  gear  should  be  kept  as  nearly  dry  as  possible  to  prevent  "grounds" 
and  "shorts."  The  mechanism  in  base  of  lamp  and  base  of  searchlight  should 
be  exposed  to  the  sun  on  hot,  sumiy  days  m  order  that  the  sun  may  help  dry 
out  any  moisture  that  may  have  accumulated. 

9.  Oil  and  grease  on  electric  contacts. 

All  contact  points  should  be  kept  free  of  oil  and  grease,  as  these  substances 
are  insulators  and  prevent  good  contact  between  cuiTcnt-carrying  surfaces. 

10.  Electric  connections. 

Should  be  kept  tight.  An  occasional  examination  and  tightening  of  loose 
connections  caused  by  vibration  will  take  care  of  this  item. 

11.  Synchronizing. 

It  will  occasionally  be  required  to  sj^nchronize  searchlights  with  the  follow- 
the-pointer  mechanism.  This  is  done  by  locking  the  searchlight  in  position  and 
making  electrical  and  mechanical  pointers  both  indicate  this  position.  The 
zero  position  is  most  convenient. 


178  THE   SEAnCHLIGHT. 

12.  Use  of  undue  force. 

Searchlights  and  control  geare  work  casil}'  and  smoothly.  They  will  not 
stick.  If  the  £carchli<;ht  sticks,  it  should  not  be  forced  to  move  as  it  will 
move  easily  after  l)ein£:;  unlocked. 

13.  Frequent  use. 

Manufacturers  of  high-power  searchlights  recommend  the  frequent  use  of 
their  product,  for  two  reasons:  First,  it  familiarizes  the  personnel  with  the 
operation  of  the  searchlight;  and,  second,  a  mechanism  of  this  kind  deteriorates 
more  rapidly  when  unused  than  when  in  frequent  operation.  Troubles  develop, 
due  to  sticking  of  parts  and  change  of  adjustments  due  to  vibration  when 
searchlights  stand  idle  for  a  long  time. 

14.  In  general,  searchlights  and  control  gears  shouM  be  as  carefully  cared 
for  as  ordnance  gear,  for  if  their  accuracy  fails,  in  battle  they  will  be  a  menace 
rather  than  an  aid  to  the  safety  of  the  ship. 


CHAPTER  15. 

VICKERS  "FOLLOW-THE-POINTER"  SYSTEM  OF  SEARCHLIGHT 

CONTROL. 


VICKERS  SYSTEM. 

An  important  recent  development  is  the  control  of  searchlights  by  director 
in  a  similar  manner  as  broadside  guns  are  controlled.  This  is  efifected  as 
foUows:  Leads  are  run  from  the  director  tower  for  a  training  indicator  at  each 
searchlight.  Each  searchlight  has  mounted  on  its  control  pedestal  a  control 
indicator. 

The  director  tower  contains  a  dummy-gun  sight  with  telescope.  This 
sight  is  mounted  on  a  turntable  and  geared  to  a  transmitter  described  later. 
This  transmitter  is  connected  electrically  to  an  indicator  on  a  searchlight 
pedestal  and  moves  there,  which  indicates  the  angle  to  which  the  searchhghts 
are  to  be  trained.  Connected  by  gears  to  the  searchlight  training  control  rod 
is  another  pointer  on  the  same  dial.  When  control  handles  are  turned  until 
a  mechanically  operated  pointer  coincides  with  an  electrically  operated  pointer, 
the  searchlight  is  trained  on  the  same  target  as  the  telescope  in  the  director 
tower,  except  for  errors  of  drift  and  deflection  which  is  applied  to  guns  and 
not  corrected  for  in  searchlight  mechanism. 

On  the  training  indicator  there  are  two  dials,  each  with  electrical  and 
mechanical  pointers.  The  upper  dial  indicates  training  angles  of  360  degrees 
per  revolution  of  pointer.  The  lower  dial  pointers  are  geared  to  upper  dial 
pointers  in  a  ratio  of  60  to  1,  so  that  lower  dial  shows  training  angle  of  6 
degrees  per  revolution  of  pointer.  The  upper  dial  is  used  to  bring  guns  and 
searchlights  approximately  on  the  target,  and  the  lower  dial,  which  is  then 
thrown  into  gear,  is  used  to  train  accurately  on  the  target. 

The  first  battleship  installation  will  be  made  on  the  North  Dakota. 
A  general  description  of  this  system  is  given  below. 

"NORTH  DAKOTA'S"  SYSTEM  OF  SEARCHLIGHT  CONTROL. 

The  North,  Dakota  is  to  retain  the  original  lights  on  board  when  changed 
over,  but  the  base-gearing  arrangements  and  lamp  will  be  changed. 

The  searchhghts  will  be  made  high  power  by  removing  old  lamps,  altering 
drum,  and  supplying  Sperry  high-power  lamps.  Shock-resisting  glass  front 
doors  will  be  provided. 

The  greatest  change  will  be  made  in  the  searchlight  base,  where  practically 
all  old  gearing,  etc.,  wdU  be  removed  and  new  gearing  with  different  ratios  will 
be  put  in.  Every  precaution  possible  will  be  taken  to  eUminate  and  prevent 
lost  motion,  backlash,  incorrect  alignment,  and  wrong  indication.  This  is 
done  by  using  only  very  carefully  cut  gears,  spht  pinions  of  Ordnance  design. 

179 


180 


THE   SEARCHLIGHT. 


THE  SEAKCHLIGHT. 


181 


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is 
11. 


IN 


si"! 

iiii 
mil 


182 


THE   SEARCHLIGHT. 


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Hit 

iliki 


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THE  SEAECHLIGHT. 


183 


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illll 


p-*    •  '  ''•■■'?.sv^^;^;-i"3c, 


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184 


THE  SEABCHLIGHT. 


THE   SEAHCHLIGHT. 


185 


:5i? 

II 

i  1?  . 

5    ^ 

i 
:':■■  i^ 

186 


THE   SEARCHLIGHT, 


I  I'H 


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«;S 


THE  SEAECHLIGHT. 


187 


roller  bearings,  ball  thrust  bearings,  expansion  joints  in  shafts,  and  special 
universal  joints.  The  searchlight  control  mechanism  must  worii  with  mathe- 
matical accuracy  to  be  of  practical  use.  New  control  pedestals  were  designed, 
and  the  gears  and  bearings  in  the  control  box  are  also  of  same  refinement 
as  in  the  searchlight.     The  entire  installation  must  be  as  accurate  as  possible. 

Illustrations  show  sections  of  gears  in  the  searchlight  base,  control  pedes- 
tals, sections  of  control  boxes,  and  general  arrangement.  The  speed  of  training 
will  be  10  degrees  in  azimuth  for  each  revolution  of  the  handwheel.  The 
speed  of  elevation  will  be  2  degrees  for  each  revolution  of  the  handwheel. 

The  entire  searchhght  installation  will  be  overhauled  and  when  finished 
should  be  a  marked  improvement  over  present  control  systems.  The  search- 
fights  with  the  shutters  closed  may  be  trained  on  the  target. 


^^r 


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tr/CA'£/i5  fOLLCt^-T^JC'/'O/NTER      rffyi^^/^/TTeFt  AND 
f/V0ICA70f<    f^OTQf^ 


Fig.  IGl. 

SEARCHLIGHT  CONTROL  ON  DESTROYERS. 

All  destroyers  will  be  fitted  with  follow-the-pointer  system  of  control 
somewhat  similar  to  that  used  on  Noiih  Dakota.  Some  modifications  are 
necessary,  but  the  general  scheme  is  the  same.  Illusti-ations  showing  sections 
of  different  types  of  gear  boxes  and  general  arrangement  will  serve  to  present 
a  general  idea  of  the  installations  on  destroyers.  These,  too,  require  great 
accuracy  of  manufacture  and  installation  for  a  successful  installation. 

ELECTRICAL  PRINCIPLES. 

The  general  electrical  arrangement  is  as  shown  in  figure  164,  the  transmitter 
having  six  steps  or  segments  laid  out  in  four  circles  on  a  disk  and  arranged 
and  connected  as  sliown.  The  disk  is  geared  to  the  director-scope  turntable, 
so  that  when  the  turntable  revolves  the  disk  rotates  under  contact  fingers  and 
various  circuits  are  closed  or  opened. 

The  contact  fingers  are  connected  to  the  poles  of  the  indicator  motor  as 
shown.     The  indicator  motor  consists  of  a  cross-shaped  armature  of  soft  iron 


188 


THE  SEABCHLIGHT. 


mounted  on  a  shaft.  The  shaft  is  geared  to  the  slowing  pointer  on  the  indicator 
dial.  Around  the  four-pole  armature  are  arranged  six  fixed  poles,  connected 
as  sho\vn. 

The  motor  has  24  positions  for  one  revolution  of  armature  and  6  positions 
for  one  revolution  of  transmitter  contact  disk. 

Table  A  shows  the  various  positions  taken  by  armature  of  the  indicator 
motor  as  transmitter  contact  disk  is  revolved. 

Table  A. 


Revolutions  of  transmitter. 

Contractors  on 
transmitter 
point  No. 

Degrees  of 

Rcv(ilutl)nof 

indicatir-mjtor 

armature. 

1 
2 
3 
4 
S 
6 
1 
2 
3 
4 

s 

6 
1 
2 
3 
4 
5 
6 
1 
2 
3 
4 
6 
6 

0 
15 
30 
45 
60 
76 
SO 
105 
120 
1.15 
ISO 

ins 

ISO 
195 
210 
225 
240 
255 
270 
285 
300 
315 
3.10 
345 

Second  revolution 

Third  revolution... 

Fourth  revolution     

The  polarity  of  poles  of  motor  for  different  positions  of  contact  disk  in 
transmitter  is  shown  in  table  following: 

Table  B. — Field  pole  polarity  as  Iransmitlcr  revolves. 


Contactors 
on  pjint 
No.-. 

Rcvolu- 
tl  ms  of 
trans- 
mitter. 

Pole  No.  -. 

1 

2 

3 

1' 

2' 

3' 

1 

First 

^Second... 

S 

s 

Not  excited. 

....do 

....do 

S 

S 

\3 

Not  excited.. 

S 

S 

S 

Not  excited.. 

d. 

do 

S 

Not  excited.. 

do 

do 

S 

8 

S          ... 

N 

N 

Not  excited.. 

do 

do 

N 

Not  excited.. 

N 

N 

Not  excited. 

Do. 

Do. 
N. 
N. 
N. 
Not  excited. 

Do. 

2 

3 

4 

N     

5 

NotexclUd.. 
do 

0 

1 

Not  excited.. 
do 

N 

do 

2 

N 

N 

Before  explaining  the  operation  of  indicator  motor,  the  electric  principles 
involved  will  be  reviewed. 

When  two  magnetic  poles  near  each  other  arc  excited  with  opposite  polarity, 
one  north  and  one  south,  there  is  a  magnetic  force  between  them.  Magnetic 
"lines  of  force"  are  said  to  flow  from  the  north  pole  to  the  south  pole.  These 
lines  of  torce  follow  the  path  having  the  least  magnetic  resistance.  Magnetic 
resistance  is  known  as  reluctance  and  reluctance  of  a  magnetic  circuit  corre- 
sponds to  the  resistance  of  an  electric  circuit. 

If  some  material  of  smaller  reluctance  than  air  is  introduced  into  an  air 
gap  of  a  magnetic  circuit,  this  material  is  acted  upon  by  the  magnetic  force  in 


THE  SEABCHLIGHT. 


189 


such  a  way  that  it  tends  to  move  so  that  it  would,  if  free  to  move,  take  a  posi- 
tion wliich  would  make  the  reluctance  of  the  magnetic  path  a  minimimi. 

The  reluctance  of  soft  iron  is  about  7^  to  3-^  that  of  air,  therefore  a  piece  of 
soft  iron  in  an  air  gap  in  a  magnetic  circuit  wUl  tend  to  move  so  as  to  offer  the 
path  of  least  resistance  to  the  magnetic  lines  of  force. 

Suppose  the  motor  to  start  at  0°  and  that  transmitter  is  at  point  1. 
Referring  to  Table  II  and  figure  —  it  is  seen  that  poles  1  and  1'  are  excited  as 
sho^vn.  The  dotted  hues  through  armatiire  show  path  of  lines  of  force  and 
arrows  show  direction  of  lines. 

Suppose,  now,  that  transmitter  be  moved  to  point  2,  poles  1,  1',  2  and  2' 
are  excited  as  shown  and  the  armature  moves  so  that  lines  of  force  may  travel 


^^  i,_i      CCNTflCTOR30NP0i«T6 


OMgFMMS  SHOWIhC  P-£^CLUTlC^^  Or  INOtCrtTOR  MOTOA 


Fig.  165. 

through  as  Uttle  air  and  as  much  iron  as  possible.  This  point  is  seen  to  be  when 
the  armature  revolves  15  degrees. 

Then  suppose  transmitter  to  move  to  point  3.  Poles  2  and  2'  are  excited 
and  path  of  least  reluctance  occurs  when  armature  moves  15  degrees  more  or 
advances  to  30  degrees  from  0°  position. 

It  is  seen  that  for  each  point  that  transmitter  moves,  the  armature  rotates 
15  degrees,  or  that  one  complete  revolution  is  made  in  24  steps  or  four  revolu- 
tions of  transmitter. 

There  is  sho%vn  in  figure  165  the  successive  steps  of  motor  for  eight  points 
(1§  revolutions  of  transmitter). 

By  suitable  gearing  this  apparatus  may  be  made  to  indicate  to  any  desired 
degree  of  accuracy. 


CHAPTER  16. 
CURRENT  DEVELOPMENTS. 


FRONT-DOOR  STRIPS. 

Considorablo  trouble  has  boon  experienced  caused  by  the  breaking  of 
front-door  strips  by  the  shock  of  gunfire  when  the  front  doors  are  in  place 
during  firing.  It  is  probable  that  the  main  battery  will  be  used  in  an  action 
at  night.  Front-door  glasses  that  will  withstand  the  shock  of  gun  filing  are 
accordingly  an  essential  part  of  the  modern  searclilight. 

The  British  Navy  has  had  some  success  in  using  old  mirrors,  having  the  sil- 
vering removed,  as  front  doors.  On  account  of  their  dome  shape,  they  are  very 
strong  and  stand  great  shock  before  breaking.  So  far  all  attempts  to  use  full- 
width  strips  supported  by  springs  have  failed  to  prevent  breaking,  the  inertia 
of  the  strips  being  so  great  that  the  glass  is  shattered  before  the  springs  have 
time  to  absorb  the  shock. 

It  is  proposed  to  try  out  radial  front-door  strips  which  will  bo  only  half 
as  long  as  the  long  center  strips  now  used,  and  therefore  more  compact.  Also 
by  having  considorablo  spring  and  no  rigidly  fixed  center  point,  they  should 
give  at  each  impact  and  not  shatter  as  easily  as  our  present  type  of  strips. 
Difficulties  are  presented,  but  they  may  bo  overcome  by  accurate  manufacture. 
The  greatest  one  is  that  a  very  slight  difi"orcnce  in  angle  of  edges  is  additive 
around  the  entire  circumference,  and  when  all  pieces  are  placed  in  position  a 
gap  would  bo  left,  and  the  space  left  for  a  radial  strip  would  bo  larger  than  the 
strip,  or,  if  the  other  strips  were  slightly  larger  than  they  should  be,  the  last 
strip  would  not  go  into  place  at  all.  A  great  advantage  is  gained,  however,  in 
that  all  strips  would  be  the  same.  No  radial  front-door  strips  have  been  tried 
out  as  yet,  but  tests  are  expected  in  the  near  future. 

The  dome-shaped  front  doors  will  also  be  tested,  and  should  they  withstand 
the  shock  of  main  battery  firing  the  searchhghts,  will  be  adapted  for  their  use. 

fflGH-SPEED  BLINKER  LAMPS. 

For  a  long  time  blinker  signaling  with  incandescent  searchlights  was  ham- 
pered by  the  slow  heating  and  cooling  of  the  filament  of  the  lamp  used.  A 
decided  afterglow  was  visible,  and  unless  great  care  and  slow  sending  were  used, 
the  dots  and  dashes  merged  into  each  other,  particular^  at  the  longer  ranges. 
The  speed  was  limited  to  only  a  few  words  a  minute  and  signaling  with  incan- 
descent searchlights  was  very  unsatisfactory. 

Recently  tw.o  companies  have  been  working  on  lamps  which  will  be  of 
such  speed  as  to  allow  a  signalman  to  work  to  the  limit  of  his  speed  of  send- 
ng  or  receiving,  except  at  very  long  range.  These  companies  have  succeeded 
in  producing  a  lamp  which  is  so  fast  that  the  separate  flashes  can  be  distin- 
guished as  rapidly  as  an  operator  can  work  the  key.     Signaling  with  either  of 

190 


THE  SEARCHLIGHT.  191 

these  lamps  may  be  done  at  a  rats  of  25  words  a  minuts,  which  is  sufficient 
for  all  purposes.  One  type  of  lamp  has  a  far  less  concentrated  filament  than 
the  lamp  developed  by  the  other  company.  It  is  not  very  good  in  front  of  a 
parabolic  mirror,  for  the  effect  of  a  parabolic  mirror  in  concentrating  the  light 
depends  on  the  light  rays  emanating  from  a  source  as  concentrated  as  possible 
at  the  focal  point  of  the  mirror.  The  lamp  with  the  more  concentrated  fila- 
ment is  quite  compact  and  is  of  equally  high  speed  as  any  other  type  of  lamp, 
making  it  the  logical  lamp  for  use  in  incandescent  signaling  searchlights  at  the 
present  time. 

High-speed,  250-watt  signal  lamps  have  been  put  on  the  allowance  lists 
of  first-line  battleships,  armored  cruisers,  and  110-foot  submarine  chasers. 

CONVERSION  OF  LOW-POWER  SEARCHLIGHTS  TO  fflGH  POWER. 

Since  high-power  searchlights  have  been  developed  to  such  a  point  that 
low-power  searchlights,  in  comparison,  are  practically  obsolete  for  use  at  sea, 
it  has  been  necessary  to  provide  a  means  of  convertmg  the  greater  number  of 
Navj"  low-power  searchlights  to  high  power.  This  may  be  done  in  general  as 
follows : 

A  high-power  lamp  is  substituted  for  the  low-power  lamp,  an  inner  drum 
is  built  to  provide  for  ventilatmg  air  currents,  and  a  ventilating  motor  is  in- 
stalled. A  number  of  low-power  searchlights  are  now  being  converted  to  high 
power  m  this  way,  and  it  is  intended  to  convert  to  high  power  the  great  majority 
of  36  and  30-mch  low-power  searchlights  on  battleships  and  eruisei-s. 

A  full  description  of  method  of  convertmg  low-power  searchlights  to  high 
power  is  given  in  Chapter  7. 

66438—18 13 


o 


UNIVERSITY  OF  CALIFORNIA  LIBRARY 

Los  Angeles 
This  book  is  DUE  on  the  last  date  stamped  below. 


Form  L9-32»i-8,'57(,C8680s4)444 


iiiai TT^S,    Finrpan   of 


1x93       Engineering  - 

AS SearchlightR  and 

1918     signal  lights 
for  the   instruc- 


tion  of  officers  and 


h93 
1918 


UC  SOLrmERN  HEGtONAL  UBftARy  FACIUT/ 


D     000  326  588 


